Twitter has blocked a series of accounts on the social network that tracked politicians' tweets and alerted other users when they were deleted.

A total of 31 accounts, including one monitoring British MPs, will no longer be able to function as intended.
Twitter said the accounts broke its rules for apps connecting to the service.
The Open State Foundation, which manages the accounts, has criticised the move.
Affected accounts, which are all known as "Politwoops" accounts, include UK-focused @DeletedbyMPs and @DeletedbyMSPs.
"The majority of deleted tweets are typos which are not very interesting," Arjan El Fassed, director of the Open State Foundation, told the BBC.
"But there are a few kept in the dark which say something about their political views."
He added that the group would be reviewing possibilities for a legal challenge to the block and would also experiment with technical options that might allow them to bypass it.
Twitter's developer agreement defines how data from the application program interface (API), which allows third-party apps access to Twitter data, may be used.
One rule specifically addresses the issue of tracking deleted tweets - and says that it is not allowed.
"Recently, we identified several services that used the feature we built to allow for the deletion of tweets to instead archive and highlight them," a spokesman for Twitter told the BBC.
"We subsequently informed these services of their non-compliance and suspended their access to our APIs."
Jim Killock, executive director of the Open Rights Group, told the BBC that people had the right to delete embarrassing tweets, and Twitter also had the right to enforce its terms and conditions.
"However, equally, tweets are published in the full view of everyone so people have an absolute right to record things they think are in the public interest, especially from politicians," he added.
"There is little Twitter can do about this."
The decision could have consequences for Twitter, according to Paul Bernal, a law lecturer at the University of East Anglia.
"This might get you friends in political circles, but it'll get you enemies in the community and you need the community as well as political people," he told the BBC.


A wildfire north-west of Los Angeles has forced the evacuation of some 10,000 homes as it expands across a rugged 51 sq-mile (132 sq-km) zone, fuelled by high winds and hot weather.

Helicopters are being used to tackle the blaze, nicknamed the Sand Fire, which broke out near Santa Clarita, 40 miles (65km) from Los Angeles.
The fire has destroyed more than a dozen homes in three days.
Nearly 3,000 firefighters are working to contain the blaze.
Officials said only 10% of the fire was under control.
"This is the fifth year of an ongoing drought, so we have very extreme fire behaviour," Los Angeles County Fire Department Chief Daryl Osby told reporters. "These are not normal times."
Fire crews have also been hampered by the forested, mountainous terrain.
Over the weekend, a body was found in a burned-out car but it is not clear if the death is fire-related.
A wildlife preserve owned by actress Tippi Hedren, who starred in the Hitchcock classic The Birds, has also been evacuated. Hedren's daughter, actress Melanie Griffith, tweeted that her mother and the 40 big cats at the Shambala Preserve were safe.
Forecasters say there could be some relief in sight with cooler temperatures due to move in.
Firefighters are also struggling to contain a blaze further north, in mountains near Big Sur.
This wildfire, spanning more than 23 sq miles (59.6 sq km), forced the evacuation of more than 1,000 homes in the communities of Palo Colorado and Carmel Highlands.


Water supplies have been restored in most of Chile's capital Santiago after floods contaminated a major river providing most of the city's water.

Storms in the Andes over the weekend had flooded the Maipo river, contaminating it with mud and rubble.
Businesses and schools had to remain closed and four million people were without drinking water.
The water company said it would take time to refill 15,000km (9,320 miles) of pipes.
Officials had said the water supply from the Maipo river had to be cut until the water flowed clear.
At least three people have been killed and 19 are missing as rivers overflowed and bridges were washed away.
A 12-year-old girl was killed when the car she was travelling in with her family was swept away by a landslide in the O'Higgins region, south of Santiago.
Two more people died in Cajon del Maipo.
More than 60% of households in Santiago woke up on Sunday to find their taps running dry.
Many queued to fill buckets and pans with water provided by the authorities.
Some shops ran out of bottled water and some supermarkets reported scuffles between people eager to stock up.
Restaurants and businesses in the affected areas were ordered to stay closed and schools were also told to delay the start of the school year, scheduled for Monday.
The flooding follows months of drought and a series of deadly wildfires which burned for weeks.


Iran's ex-President Ali Akbar Hashemi Rafsanjani, a dominant figure in the country's politics since the 1980s, has died at the age of 82, media say.

Mr Rafsanjani, president from 1989 to 1997, suffered a heart attack.
He played a pivotal role in the 1979 revolution but later in life became a counterpoint to hardline conservatives.
Supreme Leader Ali Khamenei hailed a "companion of struggle" despite their differences, saying that the loss was "difficult and overwhelming".
"The different opinions and interpretations at time in this long period could never entirely break up the friendship" between us, Ayatollah Khamenei said.
Mr Rafsanjani was admitted to the Shohadaa Hospital in Tehran on Sunday, where doctors tried unsuccessfully for an hour to save him, media said.
A TV broadcaster broke into programmes to bring the news, saying Mr Rafsanjani "after a life full of restless efforts in the path of Islam and revolution, had departed for lofty heaven".
Rafsanjani: The pragmatic conservative
Mr Rafsanjani had warm relations with President Hassan Rouhani, who was seen at the hospital shortly before the death was announced. A crowd reportedly gathered at the hospital later to mourn.
The BBC's Kasra Naji says Mr Rafsanjani was a great survivor of the Iranian revolution, always managing to stay afloat in the unending political struggles between the hardliners and the moderates, always remaining influential.
In recent years, our correspondent says, he has been a central figure in the reform movement that has been trying to have a moderating influence on Iran and Ayatollah Khamenei.
He has been a mentor to President Rouhani, whom he supported after his own attempt to run in the 2013 election as a reformist candidate was rejected by the powerful Guardian Council.
Mr Rafsanjani's final role was head of the Expediency Council, which tries to resolve disputes between parliament and the Guardian Council.
The sudden death of the veteran pragmatist politician will be a major blow to President Rouhani. The president, who is preparing himself for re-election in May, has lost a valuable ally and influential figure who was a founding father of the Islamic Republic.
This explains why Mr Rouhani was the first top official to attend the hospital where Mr Rafsanjani died. Reports say Mr Rouhani was in tears.
Since the 2013 presidential election, Mr Rafsanjani has fully backed Mr Rouhani. Mr Rafsanjani was also a staunch supporter of the landmark 2015 nuclear deal with world powers.
But in Iran's complicated political landscape, his death could also mobilise pro-Rouhani moderates and reformists ahead of the election.
Ali Akbar Hashemi Rafsanjani was born in 1934 in south-eastern Iran to a family of farmers.
He studied theology in the holy city of Qom with Ayatollah Ruhollah Khomeini - who went on to lead the Islamic revolution of 1979 - and was imprisoned several times under the Shah.
In the last year of the 1980-88 war with Iraq, Ayatollah Khomeini appointed him acting commander-in-chief of the armed forces.
He was seen as the main mover behind Iran's acceptance of the UN Security Council resolution that ended the war.
Mr Rafsanjani was also a key player in the development of Iran's nuclear programme.
He was a man known for a sharp wit but who could also be ruthless.
He advocated progressive economic policies, encouraging private businesses and improving infrastructure. His own business holdings were reported to be widespread.
Mr Rafsanjani ran for a third time for president in 2005 but lost to Mahmoud Ahmadinejad.
Mr Rafsanjani became openly critical of the victorious president and in 2009, he sided with reformers who disputed that year's elections. Nevertheless, Mr Ahmadinejad won a second term.
Mr Rafsanjani continued to champion moderate causes, such as the release of political prisoners and greater political freedoms for parties prepared to work within the constitution.
Some of the members of Mr Rafsanjani's family have also made the headlines. His daughter, Faezeh Hashemi, attracted the ire of hardliners when she met a leader of the Bahai religious minority - which Iran's leadership regards as a heretical sect - last year.
And his son, Mehdi Hashemi Rafsanjani, was jailed in 2015 after being convicted of "security offences and financial crimes".


Four former UKIP general election candidates have called for the party's Welsh leader Nathan Gill to resign.

Joe Smyth, who achieved UKIP's highest vote share in Wales in 2015, said Mr Gill showed "no leadership" during its turmoil over assembly poll selections.
Another three general election candidates, two standing in May's poll, have also called for Mr Gill to go.
A UKIP Wales spokesman said Mr Gill had "stood up constantly" for "proper representation" for the Welsh members.
On Tuesday, Mr Gill announced local members would now decide the rankings for UKIP's regional list candidates, seen as the party's best hopes for winning seats.
Mr Smyth, re-selected for Islwyn at May's assembly election, said Mr Gill should have insisted the Welsh party ran whole the selection process.
There were complaints within the party about the original plan for its National Executive Committee (NEC) to have the final say.
Mr Gill has described the move to give local branches a vote over the final rankings as a "great victory" over the NEC.
But some remain unhappy that former Conservative MPs Neil Hamilton and Mark Reckless are still in the running for selection.
At the general election, Mr Smyth won 19.8% of the vote in Islwyn.
Despite being re-selected for the constituency for the assembly poll, he pulled out of the regional list selection in protest at the way it was being organised.
Mr Smyth told BBC Wales both Mr Gill and the NEC had treated members, activists and candidates with "contempt".
"He's trying to make out now that he's saved the selection process by allowing the Welsh members to vote on the candidates, it's a fallacy," he said.
"Nathan was responsible and agreed to how the selection process was going to be run at the very beginning.
"It's completely and utterly farcical."
Accusing Mr Gill of "weak leadership", Mr Smyth called for him to "resign straight away".
The criticisms were endorsed by Blair Smillie, UKIP's candidate for Alyn and Deeside at the general election.
"Nathan Gill has been terrible, he has to go," he said.
"There is no leadership in Wales, the organisation in north Wales is in disarray."
Nigel Williams, standing in the Delyn constituency in May after running for UKIP in 2015, said he had been "concerned for some time we lack leadership across Wales".
"We've let the general election momentum slip, we need better leadership," he said.
Ken Beswick, UKIP's Torfaen general election candidate added: "Nathan Gill is not suitable as a leader - he has no backbone.
"He's very close to Nigel Farage and won't stand up to him."
Responding to the criticism, a UKIP spokesman said: "Far from being weak he's actually been very determined in his commitment to ensuring the process is not controlled by party elites.
"The selection process has been deeply complex to ensure the best outcome; there will always be people dissatisfied.
"We think putting the decision in the hands of the membership is the most democratic option.
"All candidates that will be submitted to the membership have been rigorously vetted to ensure the highest calibre candidates are put forward to represent UKIP Wales."


Meet the schoolboy who's aced a top computer test - normally only taken by adults.

Media playback is unsupported on your device
18 May 2015 Last updated at 12:47 BST
Yep - if you think you're a bit of a tech whizz then just check this out.
Six-year-old Humza has become one of the youngest people to become a Microsoft Office Specialist for Office Word 2013.
He got his first laptop when he was two and a half years old, and was taught how to use it by his parents.
Leah has this report.


Seven months after a terrorist massacre in its capital city, France raises the curtain on Friday evening on one of the world's biggest sporting events.

Two dozen national football teams and at least two million foreign visitors will be here for the Euro 2016 football championships.
But how ready is the nation to focus on "the beautiful game"?
This was meant to be France's feel-good moment. But like cherries that are always hanging just out of reach, the build-up to Euro 2016 has been interrupted by one distraction after another:
Having got through all of that, on the eve of the championship, France is facing fresh strikes at the national airline, and rubbish left to rot in the street as bin-men join the rolling protests over labour reforms.
It's a wonder people have any time left to think about whether Didier Deschamps has got the right men in his defence line-up for the French national side.
But it's not as if football has been entirely out of the headlines either.
Last month, Eric Cantona implied that the French coach had allowed racism to colour his selection for the squad.  That followed an earlier scandal that saw two of the country's top players embroiled in blackmail allegations - and consequently dropped from the Euro 2016 team.
So if the mood here ahead of kick-off has been, well, muted, perhaps it's no surprise.
But there is, of course, another reason for the rather subdued atmosphere ahead of the games.
When President Hollande arrives at the Stade de France in northern Paris tomorrow for the opening ceremony, it will be a poignant moment.  Many of those watching will be remembering the night he was bundled out of the stadium during another match last November, as three suicide bombers blew themselves up outside.
It was the start of France's night of terror, in which 130 people were killed on the streets of Paris. Now, the fears of police, public and politicians as they head into the tournament hang heavy in the air.
The Euros are spread between 10 French cities, each requiring its own security plans.
One hundred thousand police, soldiers and security guards have been detailed to protect the games but, as the interior minister points out, "even 100% preparation cannot guarantee zero risk".
A leaked police document, calling for the partial closure of vast "fan-zones" set up in cities including Paris and Marseille, has been widely reported in French media.
On the eve of the tournament, workers in Paris said they were planning to stay away from the zones, considered softer targets than the stadiums themselves.
"It's fun to have the Euros in France," said Eva, a 32-year-old jurist, "but with everything that's happening, it could create more problems than anything else. It's fun in principle, but with the strikes for example, we're not going to see a good image of France."
"Even though I'm not a big football fan, I'm excited by the ambiance," said David, a finance worker in the city.
"But the recent events are on everyone's mind and there's a lot of talk about security, so the euphoria is dampened by that.  If there is a target, it will be the Euros."
While an attack would be devastating for the host nation, a peaceful, well-managed tournament would go a long way towards restoring a sense of security, something that has been missing here since the attacks last year.
Similarly, in terms of the social divisions and political disillusionment plaguing France, the games could turn out to be a unifying moment of national pride, or another opportunity to dissect the nation's disappointment.
Many here expect the public excitement to build as France heads into the opening game against Romania on Friday night.
Because, after all the logistical problems and all the discussion of security risks, this country is hungry for some good news, and those cherries still look sweet.
After all, the nation was divided and subdued in the days before the 1998 World Cup in France, and look how that turned out.


A cable-stayed bridge, described as East Africa's longest, has opened in Tanzania's main city, Dar es Salaam, to ease over-crowding on ferries.

The 680m (2,230 ft) bridge links the city centre with southern neighbourhoods across the Indian Ocean.
Tanzania's leader John Magufuli hailed it as a "liberation" for residents in the city of more than four million.
The Chinese firm which built the $140m (£98m) structure says it is East Africa's longest cable-stayed bridge.
It is also the first toll road in Tanzania. The prices have yet to be set - vehicles and motorcycles will have to pay, pedestrians and bicycle will have free passage.
Correspondents say until now commuters' only option to cross over the creek to the Kigamboni suburbs was in badly maintained ferries. - and they are often held up for hours because of breakdowns.
Motorists also take their cars on to the ferries, and some have fallen into the sea as the vessels leave as they are not always properly loaded.
The bridge links to an area earmarked in 2010 for an ambitious plan to build a satellite city, known as the Kigamboni New City development.
The government also hopes that it will boost tourism, making it easier for people to go to beaches on the other side of the city.
At a ceremony to open the bridge, Mr Magufuli described the seven-lane cable-stayed bridge as the only one of its kind in central and East Africa.
"It has never been built before. Even if you go to Uganda, Democratic Republic of Congo [and] Kenya, there is no bridge like this," he added.
He said it should be named Nyerere Bridge after Tanzania's first President Julius Nyerere, saying the idea was first mooted by him.
Mr Nyerere led Tanzania, or what was then known as Tanganyika, to independence from the UK in 1960.
He governed the country until his retirement in 1985, and died in 1999.


Carlos Tevez accepts it will be "impossible" for him to leave Manchester City before the end of the transfer window, BBC Sport understands.

The 27-year-old had been adamant he would leave the club to be nearer to his two daughters in Argentina.
But a source close to the player told BBC Sport: "It will be impossible for Carlos to leave and he knows that."
He added that Inter Milan had made an offer for the striker, but it had fallen short of City's valuation.
The summer transfer window closes at 2300 BST on Wednesday.
Staying at Eastlands will mark something of a comedown for Tevez, who released a statement in July making clear his desire to leave City for family reasons.
A few weeks later, City thought they had agreed a deal with Corinthians for the sale of the striker, only for the Sao Paulo-based outfit to pull out because they could not finalise the transfer before the close of their international transfer window.
Inter Milan have also been consistently linked with the player, but instead opted for Atletico Madrid's Diego Forlan to replace Samuel Eto'o.
A combination of the fee wanted by City for Tevez and the player's salary demands seem to have warded off potential suitors.
Tevez is yet to start a game for City this season, with Sergio Aguero and Edin Dzeko preferred in attack by manager Roberto Mancini.
The forward has also lost the club captaincy to Vincent Kompany, while his place in the Argentina national side has again been taken by Aguero.
Tevez signed a five-year deal with City in July 2009, having moved to the club from Manchester United.
He submitted a transfer request last December, before withdrawing it and helping City finish third in the Premier League table.


Police in England and Wales are conducting a week-long crackdown on motorists who use their mobile phones while driving.

The operations will include dedicated patrols and messages on road signs.
The move follows government plans to double fines and points for using a mobile while driving.
The National Police Chiefs' Council said the campaign aims "to make 'driving distracted' as socially unacceptable as drink driving".
The national week of action comes after a previous one in May, which the police said resulted in the detection of 2,323 offences across the week.
It comes after an RAC survey in September suggested the number of motorists illegally using mobile phones while at the wheel was rising.
Of the motorists asked, 31% said they had used a handheld phone behind the wheel compared with 8% in 2014.
As part of the latest campaign week, police officers will work together with paramedics to educate the public on the risks of using phones while driving.
The officers on the dedicated patrols will be using unmarked vans, helmet cams, high-seated vehicles and high vantage points to catch offenders, the police said.
There will also be social media videos and messages, schemes enabling "community spotters" to target repeat offenders, and messages which will be displayed on commuter routes telling motorists to leave their phones alone.
Paul Newman is the founder of charity Handsoff. His sister, Ellen, was killed by a driver who was using a mobile phone in 2006.
Mr Newman told BBC Radio 5 live "all the policing in the world" would not work and that the industry had a "huge responsibility" in fixing the problem.
"This is just the beginning, the car has been bombarded by technology and nobody is taking notice of it.
"It's worse than ever out there and it's never going to stop. There will be a crackdown but that will go away, give it a few weeks and back to normal. It won't work."
He told the programme the act of motorists using mobile phones at the wheel should be treated worse than drink-driving.
Chief Constable Suzette Davenport from the NPCC said tackling mobile phone use by drivers needed "innovative approaches".
"When you're getting in your car, remember don't put others at risk - keep your eyes on the road and your hands on the wheel."
Police should target the persistent offenders just like any other crime, AA president Edmund King told BBC Radio 5 live.
Drivers are "addicted" to their phones and there are lessons to be learnt from drink-driving and seatbelt campaigns, he said.
Mr King added it was crucial to have enforcement behind any "hard-hitting" campaign.
People checking social media and texting is much more common than taking calls at the wheel, PC Derek Kitcher of Gwent Police told BBC Radio 5 live's Breakfast programme.
He said most offenders do not realise that a police car is next to them until an officer beeps their horn.
Fellow officer Sgt Leighton Healan told the programme it was something that was becoming socially unacceptable and was a "dangerous pastime".
Drink-driving was a personal choice whereas mobile phone usage was almost a spontaneous offence, he said.
"What we want to do is educate people, raise awareness around the use of mobile phones and prevent it in the first place. As a police force I'm not always keen to issue that fine if education is better served."


A show of hands was what it took to decide the fate of two alleged rapists in Ukraine's rebel east.

Residents of Alchevsk, a city in the Luhansk region, had been urged to attend the "First People's Court" on 25 October.
The separatist "Prizrak" battalion (ghost), which controls the area, said it had conducted its own investigation into the alleged crimes and invited everyone to condemn the suspects.
Speaking on the phone from Alchevsk, a fighter using the nom de guerre Smuggler told me he was present at the "trial", and he was proud of it.
"I believe criminals and scumbags should be erased from the face of the Earth," he said.
"We all believe that," a comrade could be heard in the background.
"I've met their victims," said Smuggler. "They are devastated. We live under emergency laws, we have a lot of crime, we have no proper courts at the moment, so our people create 'people's justice'.  I hope after this election we will have proper authorities, laws and courts."
Tanay Cholkhanov, a journalist sympathetic to the rebels who was embedded with the battalion at the time, attended the so-called trial and said it was a "complete farce".
"Most people who were there did not understand what was happening. It was tragic," he said.
The battalion's video of the trial, posted online at the weekend, shows some 340 people present, in a town whose pre-war population stood at more than 100,000.
The video shows the battalion commander, Alexei Mozgovoi, using the opportunity to issue a warning to all residents.
"Too many women go to restaurants," he said. "What kind of example do they show to their children? From now on, we will arrest all women we find in restaurants and cafes."
Incredulous gasps are heard from the audience.
The video shows how both suspects were presumed guilty on the basis of evidence presented by battalion investigators.
One was spared the death penalty and condemned to being sent to the front line, to "redeem himself and die with honour".
The other was sentenced to death by firing squad, despite desperate pleas from his mother, present in the audience.
By a large majority, the suspect is sentenced to death. "Good people, spare him," the man's mother screams. "Blame me, I am the one to blame!"
The battalion confirmed to the BBC that both convicts were currently held in custody and the sentences were to be carried out in the next few weeks.
The "Prizrak" battalion is reported to number some 1,500 men and controls an area with a population of 10,000 civilians.
"They intimidate these civilians, says Tanay Cholkhanov, who believes Commander Mozgovoi should be brought to justice.
But in the areas of eastern Ukraine now run by rebels, justice lies in the hands of those in power.


Fewer tourists by ferry travelled to this year's TT races  because a vessel was unavailable, its operator said.

Numbers have fallen by 6% since last year, said the Steam Packet Company.
Figures show 13,228 motorbikes and 35,500 passengers travelled to the 2016 race festival, compared with 14,055 and 36,000 respectively in 2015.
A spokesman said the downturn was "anticipated" because a fast craft, normally used to carry fans from Northern Ireland, was unavailable.
Steam Packet Chief Mark Woodward said: "Suitable vessels for the ports we serve are simply not available for short-term charter, so we had anticipated this situation and taken steps to mitigate the impact.
"Substantial investment in a removable mezzanine deck for Manannan created additional capacity to carry more motorcycles.
"Extra room for visitors and their vehicles was also made available on Ben-my-Chree thanks to the charter of MV Arrow, which took over freight duties".
The Steam Packet company said reservations for next year indicate "strong interest" with 3,500 bookings made already for 2017.


More than five emergency vehicles have crashed a day on average in the West Midlands in the past three years.

Figures obtained under Freedom of Information laws showed 5,992 crashes were recorded between 2012 and 2014.
During that period, Birmingham student Xuanwei Zhang died after being hit by an unmarked police car in Birmingham in April 2012.
Also in 2012, two men had to dive out the way after a fire engine smashed into a phone shop in Birmingham.
Owner, Jamil Mahmood, said: "There was a fire engine doing a three-point turn and it crashed into the shop, narrowly missing one of my customers and a family member.
"It missed them by inches, they had to jump out the way."
West Midlands police, fire and ambulance services recorded 2,728, 281 and 81 crashes respectively, the figures show.
Police figures showed 64 of the force's vehicles were written off in crashes.
More than 350 people suffered injuries ranging from broken ribs, whiplash and a ripped spleen, it also confirmed, but the figures did not include the death of Mr Zhang.
In one crash in Dudley last year, two police officers were injured when a man drove into the side of a police car.
An inquiry is also taking place into the death of Harry James Kirkham.  Mr Kirkham was hit by a police car in Birmingham in March this year, although this is outside the timeframe for this data.
West Midlands Fire Service said most accidents involved vehicles travelling at "slow speed".
"We continue to implement measures and awareness campaigns to reduce these," it said in a statement.
The ambulance service said crews are highly trained but rely on the help of other road users.
"The majority of collisions are down to drivers either panicking when they hear a siren or see a blue light, or not being aware of blue-light vehicles using the road," a spokesman said.
A police spokesman said it was not clear why Mr Zhang's death had not been included in its figures.
Staffordshire Police recorded 912 while Staffordshire Fire service recorded 120.
Staffordshire Police Supt Mick Boyle said they constantly monitored the driving standards of employees. The county's fire service has declined to comment.
In Warwickshire, there were 546 crashes involving police vehicles and 102 involving fire vehicles.
West Mercia Police recorded 1,143 crashes while Shropshire Fire and Rescue recorded 68.
A spokesman for both police forces said officers are sent for retraining on a regular basis if required, and future driving performance is monitored to ensure no further incidents are recorded.
The spokesman added that due to the nature of the role of the police, damage was inevitable.  He added that in the future, the fleet would be fitted with a telematics system which will mean accidents and incidents can be monitored in greater depth.


Negotiations are taking place to allow squatters who have been using a former car showroom as a homeless shelter to stay temporarily.

Campaigners say the former Volkswagen garage - owned by Wadham College - is "Oxford's unofficial homeless shelter".
Leaseholder Midcounties Co-operative said it was "very confident" it could reach an agreement.
It is trying to agree a deal that would allow the squatters to remain until April when its lease ends.
Kevin Brown, group general manager at The Midcounties Co-operative, said: "In April we have a legal obligation to hand the site back, with vacant possession, to our landlord Wadham College.
"To ensure we're able to meet that requirement, we will request a repossession order but our preference is not to use it."
Campaigners have asked for the site to be officially designated as homeless housing.
However, Wadham College hopes to redevelop the building into student accommodation.
Lewis Cairns, who is homeless and has been living in the squat, said: "It's a bit of a godsend really, I feel like I can get somewhere now.
"I can start applying for university and get things done."
Last week, Wadham College said it was "exploring everything" and had not decided whether to take legal action.
It added its primary focus was the "safety implications" for the homeless who had moved in and said it had a longstanding relationship with the Gatehouse homeless project.
A statement said: "The college will be making every effort to speak to representatives of this homeless group as well as local residents, safety experts and the site developers."


Star Wars: The Force Awakens has unseated Avatar to become the top-earning film of all time in North America, Disney says.

The studio claims the JJ Abrams film has passed the $760.5m (£520m) taken by Avatar over its lifetime, but has yet to give official figures.
Last month, Star Wars: The Force Awakens became the fastest film to take $1bn (£674m) at the global box office.
But Avatar - released in 2009 - still holds the global record.
The James Cameron film took $2.8bn (£1.9bn) across the world, as compared to The Force Awakens worldwide earnings of $1.6bn (£1.09bn) to date.
The Force Awakens is already the fourth highest-grossing global movie of all time after just three weeks in release, but analysts believe it will have to play well in China, where it opens on Saturday (9 January), to beat the record set by Avatar.
Disney thanked its fans for helping it clinch the domestic record, saying that without them "there is no Star Wars."
"There has indeed been an awakening - and it's all thanks to you," Disney said, in a statement released on Wednesday.
The seventh instalment in the Star Wars series returns the action to "a galaxy far, far away" some 30 years on from the action of 1983's Return of the Jedi.
The hotly-anticipated film, which reunites the original trilogy stars, Harrison Ford, Carrie Fisher and Mark Hamill alongside newcomers including Britons Daisy Ridley and John Boyega, scored the biggest US Christmas Day box office takings in history with $49.3m.
It also smashed the record for the biggest box office debut weekend globally - when it opened on 16 December, in most countries - with ticket sales of $529m.


"I don't think health and safety allows us to match Victoria's Diamond Jubilee beacon in 1897 which was pretty monstrous."

So says Rob Havard, the acting director of the Malvern Hills Conservators, the charity that looks after the area.
He may not be able to match his Victorian predecessors for scale, but the bonfire he has planned for the top of the Worcestershire Beacon will still be one of the most visible in the county.
If you stand at the top of the 425m (1,395 ft) Worcestershire Beacon and look east the next highest hills are the Urals in Russia.
For this reason the hill has been used for the beacons after which it is named since Norman times.
The 30ft (9m) Jubilee beacon will be made from pallet wood and scrub collected by the Conservators.
The Malvern Hills are now designated as an Area of Outstanding Beauty, and special permission had to be obtained from Natural England before the plans went ahead.
Mr Havard said they will take special precautions to ensure the hill is not damaged by the bonfire.
"We'll be putting down a barrier layer underneath and then we'll put a layer of sand on top of that, then another membrane and the fire goes on top," he said.
An officer from the Conservators will stay at the bonfire site throughout the night to ensure the fire doesn't spread to other parts of the hills.
The building of the bonfire will be take place from 08:00 BST on Jubilee day, to foil any would be arsonists.
The beacon will be lit by 77-year-old Tony Cotgreave, who now lives in Alsager, Cheshire.
As a teenage Scout living in Malvern he lit the bonfire at the Worcestershire Beacon built to celebrate the Queen's coronation in 1953.
Mr Cotgreave also helped guard the bonfire as it was being built, sleeping out at the top of the hill.
"There used to be a cafÃ© on top of the Malvern Hills which was derelict at the time, so a couple of scouts including myself slept up there for a couple of nights before the lighting of the fire to safeguard it," he said.
He remembers their stay at the top of the hill as anything but pleasant as the weather was "atrocious" and the derelict cafe had clearly been used by the sheep who roam the hills.
Mr Cotgreave said lighting the bonfire also proved eventful: "I climbed a short wooden ladder and set light to some brushwood that had been soaked in paraffin - it flared up and I got down the ladder a sight quicker than I got up it."
He said it was a "double honour" to be involved in the beacon lighting for a second time, especially as his granddaughter was coming from Sweden and his cousins from America for the event.
"I'm just hoping and praying for different weather from 1953," he added.
Approaching foes
The massive Victorian beacons were a spectacular site, according to a correspondent called Worcestershire Sauce, reported in the Malvern Advertiser in July 1887.
He described how "the leaping cracking flames and the close volume of breeze-blown smoke circling and spreading over the dark outlined hillside, the town lit lit by the powerful ruddy glow of the blazing hills, the dark masses of the people silhouetted against the glare, all made for a never to be forgotten sight".
He also watched as the gorse covering the Worcestershire Beacon was set ablaze as the fire spread.
The beacon can be clearly seen from a great distance.  A letter writer in the same Malvern Advertiser watched the one lit for Queen Victoria's Golden Jubilee from the top of the grandstand on Worcester racecourse, 10 miles (16km) away.
He added that it was "a sight to be remembered" and showed the value of beacons "should people need to be appraised of approaching foes".
A system of organised warning beacons on high points across the country, including the Malverns, had been in place since Norman times.
A call to arms sent by beacon would travel far faster than a messenger on horseback.
The system was not foolproof though - in 1545 rumours spread of a French landing on the coast, the beacons were lit, and the Worcestershire militia tramped all the way to Swindon before they were told it was a false alarm.


French President Emmanuel Macron has unveiled a gender-balanced cabinet in accordance with an earlier pledge, with 11 of 22 posts taken by women.

Sylvie Goulard is defence minister while Olympic fencing champion Laura Flessel is sports minister.
Bruno Le Maire is economy minister, Gérard Collomb is interior minister and François Bayrou is justice minister.
Mr Macron's decision to pluck figures from across the political spectrum has sent the French right into disarray.
Mr Le Maire is a conservative moderate, Mr Collomb is the Socialist mayor of Lyon and Mr Bayrou is a veteran centrist.
Some 170 elected officials from the right were earlier criticised by hundreds of other lawmakers after they signed a statement backing Mr Macron.
One accused Mr Macron of "blowing up" the political landscape.
France's new president will hope his team delivers a majority in parliamentary elections next month.
He delivered on his pledge of a cabinet of parity - though only one of the top five posts, that of defence, went to a woman.
Other ministerial appointees include Jean-Yves Le Drian, in charge of defence under President François Hollande, who will become foreign minister. Nicolas Hulot, a well-known environmentalist, becomes ecology minister.
Long-time Macron supporter and campaign manager Richard Ferrand is rewarded with the territorial cohesion portfolio.
Other ministerial appointees include:
Marlène Schiappa, whose successful blog Maman Works saw her dubbed the "spokeswoman for working mums", becomes junior minister for equality between women and men.
As well as the political centre ground, Mr Macron also took in figures from the left.
The announcement was delayed after candidates were background-checked for their tax records and any potential conflicts of interest.
It comes amid consternation among forces of both the left and right at Mr Macron's offer to join him in his political project of bridging the divide.
After he named Republican Edouard Philippe as prime minister on Monday, more than 170 elected conservatives agreed to sign up to the project, some claiming they were witnessing the "transformation" of politics.
However, the Republican party rejected Mr Macron's "outstretched hand" ahead of upcoming election.
It announced it was expelling Mr Phillipe, along with new economy minister Bruno Le Maire, and Gérald Darmanin, who took responsibility for public accounts.
In response, Mr Le Maire said he had "chosen to serve" and said he believed "France is worth more than all the [political] parties".
Ahead of the June legislative elections, Republican campaign chief François Baroin accused Mr Macron of "putting a bomb under politics rather than remodelling it".
The initiative has also been criticised on the left, with defeated Socialist presidential candidate Benoît Hamon among the dissenters.
"Who can think that the left will pull itself together if it is part of a coalition led by a member of the Republican party?" he said.
Separately, Mr Macron met the president of the European Council, Donald Tusk, to start talks on an "ambitious European policy".
The new president had promised to reform the EU while remaining an ardent supporter.
Mr Tusk told the French leader: "Europe needs your energy, your imagination and your courage."


A number of attacks took place in Paris, France, last Friday.

17 November 2015 Last updated at 18:15 GMT
More than 120 people were killed by the extremist group that calls itself Islamic state.
Loads of you have been in touch to ask why.
Martin asked BBC security correspondent Frank Gardner to answer some of your questions about what happened.


Port Vale have signed Colombian winger Cristian Montano and goalkeeper Rob Lainton - both on two-year deals.

Montano, 25, arrives in Burslem following two years at Bristol Rovers.
Ex-Bolton Wanderers and Burton Albion keeper Lainton, 27, who ended last season on loan at Cheltenham, moves to Vale Park following his end-of-season release by League One club Bury.
Relegated League Two side Vale used six keepers last term after starting the season with Jak Alnwick in goal.
Alnwick left the club at the end of January, joining Scottish top-flight club Rangers.
Vale then alternated between Deniz Mehmet and Leonardo Fasan, on loan from Celtic.
They also used Ryan Boot, with Harry Pickering on the bench, when Alnwick got injured, when summer signing Miguel Santos made the last of his three appearances.
But Santos then also departed the club in January, Mehmet was released at the end of the season and Fasan has returned to Celtic.
Vale are expected to make further signings this week, including another keeper.
Montano, who began his career at West Ham United, had spells at Notts County, Swindon, Dagenham & Redbridge, Oxford United and Oldham Athletic before returning to Colombia to join América de Cali.
This came after he was sacked by Oldham in December 2013 after being arrested over allegations of spot-fixing, but he was never charged and the case was dropped in January 2015. He then returned to England to join Bristol Rovers in 2015.
Meanwhile, 17-year-old Vale defender Luke Dennis has followed the lead of fellow scholars Joe Slinn, Mike Calveley and Charlie Walford in signing his first professional deal with the club - a one-year contract.
Find all the latest football transfers on our dedicated page.


The mastermind behind the Hatton Garden jewellery raid has been taken to hospital days before his sentencing, his family has confirmed.

Brian Reader, 76, fell seriously ill at Belmarsh Prison, where he is being held, and was taken to nearby Queen Elizabeth hospital on Wednesday.
Reader, the oldest member of the gang, had pleaded guilty to conspiracy to commit burglary last September.
He is due to be sentenced on 7 March with six others over the £14m raid.
A Prison Service spokesperson said: "An HMP Belmarsh prisoner was taken to hospital on 24 February. He remains there in order to receive treatment for an ongoing medical condition.
"Appropriate security measures are in place."
Reader's solicitor Hesham Puri said Reader was being treated for "a number of issues" at the south-east London hospital and it was "unlikely" his client would be able to attend the sentencing hearing at Woolwich Crown Court.
The "largest burglary in English legal history" took place at Hatton Garden Safe Deposit Ltd in London's jewellery quarter over Easter last year.
The gang raided safe deposit boxes for jewels after boring into the vault.
John "Kenny" Collins, Daniel Jones and Terry Perkins pleaded guilty to conspiracy to commit burglary.
Carl Wood and William Lincoln were convicted of conspiracy to commit burglary and conspiracy to conceal, convert or transfer criminal property.
Hugh Doyle was found guilty of concealing, converting or transferring criminal property.
Another thief, known only as "Basil", is yet to be identified and is still at large.
Reader was also involved in the £26m gold bullion Brink's-Mat robbery three decades ago.


Four huge offshore wind farms combining hundreds of turbines have been approved off the east coast of Scotland.

The developments in the Forth and Tay region could provide 2.284 gigawatts of power, enough to power over 1.4m homes every year.
Government consent was granted under strict conditions to mitigate any potential environmental impact.
It is estimated the four developments will produce carbon savings of 135m tonnes of CO2 over their lifespans.
While the offshore developments have won the backing of green groups including Friends of the Earth Scotland, the Royal Society for the Protection of Birds Scotland voiced fears over the proximity of seabird colonies.
The Neart na Gaoith wind farm east of the Fife Ness coastline will have up to 75 turbines, generating 450 megawatts (MW) of power.
The Alpha and Bravo Seagreen developments combined will consist of up to 150 turbines, around 27-38km off the Angus coastline, and could generate 1050MW.
And the Inch Cape development, also off the Angus coastline, will total no more than 110 turbines, generating 784MW.
Energy minister Fergus Ewing said renewable energy was "extremely valuable" to Scotland's economy.
He added: "These wind farms alone could generate a combined gross value added of between £314m and £1.2bn over their lifetime, and generate between 2,567 and 13,612 jobs within Scotland during the construction period.
"I am determined to ensure communities all over Scotland reap the benefit from renewable energy, which will help to reduce climate emissions."
The news was also welcomed by Friends of the Earth Scotland, the Crown Estate and Scottish Renewables.
Director Dr Richard Dixon said the approval for the developments was a "big step forward" for Scottish renewable energy.
He said: "Just these four developments could supply two-thirds of Scotland's electricity needs with clean, green energy on windy days.
"These scheme represent as much capacity as Scotland's current nuclear reactors - together with other renewables, these wind farms will ensure we not only meet all of our own demand, but we have a strong surplus of green electricity to export to England, Northern Ireland and beyond."
Ronnie Quinn, lead for energy and infrastructure in Scotland at the Crown Estate, which manages the UK's seabed, said the plans "further cement the UK's position as a global leader in offshore wind".
And Lindsay Leask, senior policy manager at Scottish Renewables, added that the consent was a "massive leap forward" for the Scottish green energy sector.
She said: "This industry has the potential to generate massive amounts of renewable power for homes and businesses and support thousands of new jobs while helping to slash Scotland's carbon emissions."
However, RSPB Scotland expressed "major concerns" over the proximity of seabird colonies to the developments.
Large colonies of gannet, kittiwake, puffin and razorbill breed along the coastlines near the wind farm sites, including the 110,000 gannet colony at the Bass Rock and puffin breeding grounds at the Isle of May.
The society said it was "inevitable" that there would be a decline in species due to seabirds colliding with turbines and displacement from foraging grounds at sea.
RSPB Scotland director Stuart Housden said it was "extremely disappointing" to see approval for developments which "put so many thousands of Scotland's seabirds at risk".
He said: "If the models and assessments of potential damage prove accurate, these windfarms would be amongst the most deadly for birds anywhere in the world.
"RSPB Scotland wants to see the development of offshore wind in Scotland but it must not be at such massive cost to our internationally important seabirds."


Highland Council has estimated that the gross total cost of replacing all its road structures, if it ever had to, would run to more than £650m.

The local authority is responsible for about 2,200 bridges and culverts and more than 1,000 walls on its 4,195 miles (6,752km).
It has the most road structures and the longest road network of Scotland's 32 local authorities.
It is having to spend £350,000 on improvements to four bridges.
They are Struy, Achfary, Blackburn and Coronation.
Community services committee chairman Allan Henderson said: "We have a huge number of bridges across our road network in the Highlands and many of these are vital to connect local communities, particularly in rural areas.
The council continually has to prioritise where limited resources can be allocated to carry out essential repairs.
He added: "Recognising the importance of our roads across the Highlands, it is our intention to propose a significant programme of investment in our roads and bridges for agreement at council in December."


The Lord's Resistance Army (LRA) rebel force has abducted 217 people since January in the Central African Republic (CAR), a campaign group says.

This is nearly double the number of abductions carried out by the LRA in 2015, LRA Crisis Tracker added.
The abductees, including 54 children, may have been forced to become soldiers or sex slaves, it said.
The LRA appear to be trying to "replenish" its forces because of military setbacks, the group added.
It has been hit by a spate of defections, and arrests since foreign forces began pursuing it in 2011.
The US deployed 100 special forces to support thousands of African troops searching for LRA commanders.
The International Criminal Court has issued an arrest warrant for its leader, Joseph Kony, to stand trial for war crimes.
In December, his former bodyguard, George Okot, defected.
The LRA had lost a "large chunk of its fighting force", and seemed to be trying to rebuild its force through abductions, said Sean Poole of the Invisible Children campaign group, which is part of LRA Crisis Tracker.
The spike in abductions in the first three months of this year signalled a "huge change in the modus operandi" of the LRA, he told the BBC's Newsday programme.
The LRA was formed in northern Uganda nearly three decades ago, but retreated to CAR and other countries as it came under military pressure.
LRA Crisis Tracker says it is responsible for more than 100,000 deaths, and a similar number of abductions.


A replacement for the sculpture of a Celtic sea god that was stolen from Binevenagh mountain is ready to be installed.

Manannán Mac Lir was taken from its spot on the mountain near Limavady, County Londonderry, in January.
It was later found by a rambling group who then sought the help of soldiers on a training exercise.
A date has not yet been set for the new statue to be erected.
A spokesperson for Causeway Coast and Glens Borough Council said: "We are delighted that Mr Sutton has completed the new sculpture of Mannanán Mac Lir.
"We look forward to the return of the artwork at Gortmore viewpoint in the very near future."
The sculptor John Darren Sutton told the BBC he was "delighted".
"It takes a while to get these things right so I'm happy that he is ready.
"He'll be on his way to Limavady and the mountain soon."
The original sculpture, which had been badly damaged, was found about 300m from Gortmore viewpoint.
Thieves left a wooden cross in place of the statue with the words "you shall have no other gods before me".
The fibre glass statue sparked an online campaign and a missing persons appeal by police.
Former Limavady Borough Council agreed to replace the statue, at a cost of £10,000.
SDLP councillor Gerry Mullan said: "I'm very excited at the prospect of Manannán Mac Lir returning home.
"People from all over the world came to get photographs with it. Lets hope that happens again.
"I urge people to take care of him and we hope a similar act doesn't happen again.
"Santa may even stop by to see him."


The man who has overseen British sailing's Olympic successes for the past 15 years has been named as British Cycling's new performance director.

Under Stephen Park, Britain's sailors have amassed 23 Olympic and Paralympic medals, and finished top of the medal table at this summer's Rio Games.
The 48-year-old Scot has now been tasked with continuing British Cycling's recent dominance.
"I feel enormously privileged and excited," Park said.
Britain's cyclists have been a dominant force on the track in particular in recent years, but have also had success on the road, in mountain biking and BMX.
They won 33 medals at this summer's Rio Olympic and Paralympic Games, 18 of which were gold.
Sir Dave Brailsford was the last person to fill the role of performance director at British Cycling.
He left in April 2014 to focus on Team Sky, with head coach Shane Sutton moving into a new role as technical director.
Sutton left 100 days prior to the Rio Olympics amid allegations of sexism - he was later cleared of eight of nine allegations against him - with programmes manager Andy Harrison taking on his responsibilities.
"Clearly cycling poses very different challenges to sailing, but it's a sport I am very passionate about from a personal perspective. I'm looking forward to meeting its challenges head on," Park added.
Find out how to get into cycling with our special guide.


Oil giants Shell and Taqa have announced plans to cut hundreds of North Sea jobs.

Shell UK plans to cut 250 posts from its North Sea operations and change offshore shift patterns, as part of a drive to manage rising costs.
Staff and agency contractors based in Aberdeen and on installations in the North Sea were informed on Thursday.
Earlier, Taqa said it planned to cut about 100 jobs because of the "challenging" time facing the industry.
Shell's upstream vice president for the UK and Ireland, Paul Goodfellow, said: "The North Sea has been a challenging operating environment for some time.
"Reforms to the fiscal regime announced in the budget are a step in the right direction, but the industry must redouble its efforts to tackle costs and improve profitability if the North Sea is to continue to attract investment."
He added: "Current market conditions make it even more important that we ensure our business is competitive.
"Changes are vital if it is to be sustainable. They will be implemented without compromising our commitment to the safety of our people and the integrity of our assets."
The cuts are in addition to 250 redundancies announced by the company last August.
Taqa said it was consulting with the workforce on plans to cut 100 jobs - mostly contractors and consultants working in onshore positions.
It is the latest in a series of redundancy announcements by North Sea operators, following a fall in oil prices and rising production costs.
BP and Chevron are among the other firms to have cut jobs.
A Taqa spokesperson said: "Taqa's UK North Sea business, along with the industry as a whole, is operating in a challenging environment.
"As part of our focus to ensure Taqa's sustainable future in the UK, regrettably it is necessary for us to scale back the number of people working with us.
"The impact of these changes will predominately be on contractors and consultants.
"We are currently proposing a reduction of around 100 onshore positions, but the process will take a number of weeks and involve consultation with our workforce.
"Our workforce are fully informed on the proposed changes and we will work to support and guide them through the process."
Responding to the announcements, Oil & Gas UK's economics director Mike Tholen said: "The new Oil and Gas Authority is progressing apace and the Budget announcement last week laid the foundations for the regeneration of the UK North Sea.
"As we said at the time, however, it is crucial that the industry itself now builds on this by delivering the cost and efficiency improvements required to secure its competitiveness.
"While these are tough decisions to take given the impact on people, the measures are being taken by many companies and will allow the UK to benefit in the long-term from a boost to energy security, hundreds of thousands of highly skilled jobs and billions of pounds worth of supply chain exports."
The union Unite claimed there was a "dangerous and quickening race to the bottom" on jobs, terms, conditions and safety in the UK's offshore oil and gas industry.
Unite Scottish secretary Pat Rafferty said: "Only last week the industry got everything it wanted from the Chancellor in the form of a Â£1.3bn tax break, which industry voices claimed was necessary to boost growth and sustainability.
"Instead the cut and gut of ordinary offshore workers' livelihoods and terms and conditions goes unchallenged while executive pay across oil company majors goes through the roof."
The job loss announcements came as a report by energy data analysts Wood Mackenzie warned that global oil and gas exploration activity could be "significantly curtailed" this year as a result of average budget cuts of 30% by firms in response to low oil prices.
However, it said average exploration costs would fall by 33%, softening the blow of the cuts.
Wood Mackenzie added that although overall well numbers would dip this year, drilling activity was set to recover in 2016 as many explorers seized their chance to drill at lower costs.
Andrew Latham, from Wood Mackenzie, said: "Rising costs are not a new problem for explorers.
"Over this decade, inflation has more than offset price gains and left much of the industry struggling to create value.
"Now that prices have fallen sharply, this problem has become acute. In the short term, many explorers will react by simply spending less. But what they really need is lower costs."


The Angolan capital, Luanda, remains the world's most expensive city for expatriates, according to an annual survey by consultancy Mercer.

The city has held the number one spot for the past three years because of the high cost of rent, imported goods and security in the oil-rich nation.
However, the rest of the cost of living rankings saw significant shifts due to exchange rate fluctuations.
Asian cities now account for half of the top 10 costliest destinations.
Hong Kong rose to second place and Singapore remained in fourth because of their expensive property and rental markets.
Shanghai, Beijing and Seoul also made the top 10.
Chinese cities now account for nine of the top 30 most expensive cities because of the growing strength of the renminbi.
Tokyo fell out of the top ten for the first time after the yen weakened against the US dollar because of Japan's stimulus program.
It used to top the rankings, but is now in 11th place, down from seventh last year.
N'Djamena, the largest city in Chad, also used to rank consistently highly, but dropped from second to 10th place.
The least expensive cities are Bishkek in Kyrgyzstan, Windhoek in Namibia and Karachi in Pakistan, Mercer said.
The rest were located mostly in Eastern Europe, the Middle East and Africa.
The most expensive European cities are found in Switzerland, with Zurich, Geneva and Bern occupying third, fifth and ninth place in the rankings.
This comes after the Swiss franc jumped following an unexpected move by the country's central bank to remove a ceiling on the currency's value.
But many western European countries saw their cost of living fall due to a slide in the value of the euro.
London remained in 12th spot in the rankings, while Copenhagen slipped nine places to number 24.
The biggest fall from the top 10 was Moscow, which dropped 41 places to 50th because of the depreciation of the rouble following US economic sanctions.
"European currencies have weakened against the US dollar, which pushed most western European cities down in the ranking," said Nathalie Constantin-MÃ©tral, principal at Mercer.
"Additionally, other factors like the eurozone's economy, falling interest rates, and increasing unemployment have impacted these cities".
Across the Atlantic, New York remains the most expensive city in America, followed by Los Angeles, San Francisco and Washington.
Mercer has been conducting the survey for more than two decades using New York and the US dollar as its base city and currency.
The consultancy compares the cost of a basket of over 200 goods and services, including food, transport and accommodation.
The results are then used by governments and multinational companies when determining salary packages for employees being sent overseas.
Several companies, including the Economist Intelligence Unit and ECA International, issue cost of living surveys with differing results.


The Pope's closest adviser on ecology has urged Catholics to join global climate marches planned for Sunday.

In an internal letter to bishops, Cardinal Peter Turkson says people should be "encouraged" to exercise their "ecological citizenship".
The letter says that climate negotiators meeting in Paris need to hear the voice of "God's people".
Activists say the call is evidence of a step-change in the Church's approach to climate change.
Major demonstrations across the world have been planned to mark the start of the global climate conference, known as COP21.
In Paris, planned big rallies have been cancelled in the wake of the 13 November attacks which killed 130 people.
Nearly 1,000 people thought to represent a security risk have been barred from entering the country, said Interior Minister Bernard Cazeneuve.
A handful of other activists have been placed under house arrest under emergency powers introduced following the attacks.
But elsewhere protesters have taken to the streets to demand action.
Over the next two weeks, delegates meeting here are hoping to strike a new, far-reaching deal on climate change.
In his letter to around 5,000 Catholic bishops around the world, the cardinal makes it clear that relying on political leaders to achieve environmental justice is not enough.
He states that more than one million people around the world are likely to take part in climate marches on 29 November.
The marchers will be exercising "global ecological citizenship", he says, and he suggests to the bishops that they "are warmly invited to offer your support in prayer, word and action".
The letter gives contact details for the bishops on how to find out about marches in their diocese.
"If you could please encourage the faithful and many others to exercise their 'ecological citizenship', this would surely help to reinforce the humble and peaceable spirit of Laudato si', and it would spiritually express communion with the universal church," the letter reads.
Cardinal Peter Turkson is president of the Pontifical Council for Justice and Peace but is seen as the Pope's point man on climate change.
A sometimes controversial figure within the Church, he was touted as a potential replacement after Pope Benedict's retirement.
Under Pope Francis he has emerged as a leading advocate for the environment and helped write the first draft of the Pope's landmark encyclical, Laudato Si'.
The Pope has expressed his worries that the negotiating process here in Paris may fail to deliver a global agreement. He said it would be "catastrophic" if global leaders let special interest groups derail the deal.
Speaking in Nairobi earlier this week, the Pope said the world faced a stark choice to either "improve or destroy the environment".
Environmental campaigners are in little doubt that the letter to Catholic bishops is in keeping with the Pope's progressive stand on climate change.
"In the letter he is not only asking people to go to the streets, he is asking them to pray as well," said Oscar Soria from Avaaz, who are organising the global marches.
"I think it is a continuation of the Pope's narrative right now, from the encyclical, to his speech at the United Nations, then to Nairobi and then the climate march.
"It's clear sign that the Vatican is stepping up its climate battle in a way never seen before."
In Paris, an installation of "marching shoes" will be built with contributions from thousands of people. The Pope has agreed that a pair of shoes bearing his name will be part of the display.
Cardinal Turkson is expected to attend COP21 as part of the official Holy See delegation.
Follow Matt on Twitter @mattmcgrathbbc.


Final preparations have begun for what has been described as the UK's first snowsports music festival.

Groove CairnGorm, is being held on 11 and 12 March in conjunction with the CairnGorm Mountain ski centre.
The music event will be based at Badaguish Outdoor Centre, near Aviemore, but will also see performances at the ski resort.
The Scottish Freestyle Championships are due to take place on the same weekend at CairnGorm Mountain.
Lined up for Groove CairnGorm are Niteworks, a band from Skye, and hip hop acts DJ Grandmaster Flash and Spring Break.
Also due to perform are The Cuban Brothers, Prides, DJ Monki and The Elephant Sessions.
The organisers of the new music festival hope to make it a regular event along the lines of continental Europe's snowsports music festivals Snowbombing and Snowboxx.


About 2,500 police officers and military personnel have raided a suburb of Brazil's second largest city, Rio de Janeiro.

Armed security forces, wearing camouflage uniforms, swept through Niteroi, a crime hot spot in east Rio.
Violence has been on the rise in Rio since the end of the Olympics nearly a year ago, with violent gangs operating in the city's favelas.
More than 90 police officers have been killed in Rio state so far this year.
Last month the government deployed more than 10,000 soldiers and police to fight organised crime in Rio.


Japanese astronaut Kimiya Yui answered questions from children in Japan during his mission on board the International Space Station.

Media playback is unsupported on your device
8 August 2015 Last updated at 13:08 BST
He told children: "When I was a pilot, it was the same in terms of flying above the ground and watching the beautiful woods and the sea. However, it was only when I became an astronaut that I realised how small Earth is.
"The Space Station goes around the Earth in around 90 minutes... you can tell how small the Earth is, and we have to look after it.''
He also said that studying and helping your parents clean up could help them become astronauts one day.
The Space station orbits 200 miles above our planet and Kimiya is staying for 5 months.


Brazil's Bovespa stock market was briefly halted as investors reacted to corruption allegations against Brazilian President Michel Temer.

Stocks plunged more than 10% at the start of trading, prompting circuit breakers to kick in and halt dealings.
President Temer was forced to deny a newspaper report that he had given consent to paying off a witness in a huge corruption scandal.
The Supreme Court has authorised an investigation into the allegations.
On Thursday Mr Temer said in a TV statement: "I never authorised any payments for someone to be silent. I did not buy anyone's silence. I fear no accusations."
"I have nothing to hide. I never authorised anyone to use my name"
"We cannot throw so much hard work [on reforms] done for our country in the rubbish bin."
"I will not resign. I will not resign. I know what I have done."
Investors are concerned that Mr Temer's reform plans could be derailed. The Ibovespa index closed more than 8.8% down at 61,575 points.
Mr Temer is trying to get pension reforms through Congress that would mean men would have a minimum retirement age of 65, and women 62, and most people would contribute more. There is currently no minimum retirement age.
There are also labour reforms on the cards to weaken trade union bargaining powers and make hiring and firing workers easier.
"I've never seen anything like this", said one trader with decades of experience.
Trading was delayed in Sao Paulo's stock exchange and once it opened, the circuit breaker stopped all operations within just a few minutes. That has not happened since the global financial crisis of 2008.
In a fortnight Mr Temer was about to start pushing his economic reform plan through Congress.
Until Tuesday markets were very optimistic - but now many don't see how Mr Temer can keep his job if the allegations about a tape in which he condones a bribe payment are true.
What happens next? If Mr Temer keeps his job, he will need a Herculean effort to get Congress behind him again. If not, the Brazilian Congress will have to chose a new president indirectly.
Getting reforms approved is no longer a top priority for a country still in deep crisis.
On Wednesday night, the O Globo newspaper reported that Mr Temer had been recorded discussing payments to silence former House Speaker Eduardo Cunha.
Mr Temer's office said he had never requested payments to Mr Cunha, and called for a full investigation into the allegations.
Two MPs have filed impeachment proceedings against the president.
And on Thursday senator Aecio Neves, an important ally also accused in the tape recording, was suspended from Congress and had his house raided by the police.
Mr Cunha was jailed for 15 years in March for corruption, money laundering and tax evasion, as part of a major investigation dubbed Operation Car Wash.
The probe, launched in March 2014, centres on companies that were offered deals with state oil giant Petrobras in exchange for bribes, which were funnelled into politicians' pockets and political party slush funds.
Almost a third of Mr Temer's cabinet is under investigation for alleged corruption.
Mr Temer played a key role in the impeachment proceedings against his predecessor, President Dilma Rousseff, last year.
She was removed from office accused of illegally manipulating government accounts. She denies all the charges.