By Gabriel Stargardter

PARIS (Reuters) - A Telegram group called French Prisoner Rights (DDPF), created the day before a series of attacks against jails across France, is being investigated by police for clues as to who could be behind the assaults.

A graffiti tag of "DDPF" was daubed at various prisons that were attacked, raising scrutiny on the Telegram group.

The group, which has over 1,000 members, was created on April 12, the day before the first wave of attacks when vehicles were set alight in the car park of the National School of Prison Administration in Agen, and in the Sud Francilien jail south of Paris. Telegram blocked several of the messages posted by the group, as it said they "contain calls to violence."

"We are not terrorists," the group posted on Tuesday night, after the National Anti-Terrorism Prosecutor's Office (PNAT) took charge of the probe, with help from the DGSI domestic spy agency. "We are here to defend human rights inside prisons."

The group does not explicitly claim responsibility, and the French government has yet to say who is behind the attacks, saying all avenues are being explored. A senior French security source told Reuters there is currently no evidence to suggest foreign interference.

Justice Minister Gerald Darmanin, who this week announced a plan to build 3,000 prison places in pre-fabricated jails, said he believes the attacks are a reaction to government efforts to clamp down on a fast-growing drug trade fuelled by a record-breaking surge of South American cocaine flooding Europe.

However, the existence of the group and the tags led some police sources to tell Reuters that they suspected a previously unknown hard-left group.

Darmanin, widely seen as a possible 2027 presidential contender, has been a key architect of the government's counter-narcotics drive. He plans to open new high-security prisons to house France's top 100 kingpins, use video conferences for court appearances and limit inmates' family contact.

Police say prisoners run their drug businesses via smuggled cellphones that they also use to order hits on rivals. They can even order kebabs and sushi, delivered to their cells via drones, according to videos posted online and prison officials.

Asked about the Telegram group on Tuesday, Darmanin said he didn't know, nor care who was behind the slogan.

'MOBILIZE AND WAKE UP'

In its manifesto, the DDPF group said it rejected Darmanin's prison crackdown. In the group's original photo, it showed a Photoshopped image of him behind bars in a Lacoste track suit.

"This channel is a movement dedicated to denouncing the violations of our fundamental rights that Minister Gerald Darmanin intends to undermine," it said. "All prisoners in France must mobilize and wake up. The situation is grave: we are entering a dangerous and worrying era for the future of the prison population."

It said hard-won prisoner rights, such as watching TV or exercise time, were being eroded, while phonebooth costs, at 1 euro a minute, were prohibitively expensive.

"The guards who beat us, who rape certain inmates, who exert physical and psychological pressure: most suicides in prison are due to the aggressiveness of the prison administration and its code of ethics," they wrote.

The group also shared snippets from French documentaries about life behind bars, and humorous videos filmed by inmates. But it also contains more menacing messages.

"Know that our movement is spreading throughout France. All prison guards who took advantage of their power and contributed to the deterioration of prison conditions will pay the full consequences," it said.

The Justice Ministry did not immediately respond to a request for comment. Neither did Telegram.

The group's main target ultimately appears to be Darmanin and his prison crackdown.

"You, Darmanin, started the war; we just want human rights to be respected," they wrote.

(Reporting by Gabriel Stargardter; Editing by Rachel Armstrong, Philippa Fletcher)