France's justice minister on Tuesday said gun and arson attacks on at least six prisons around the country were acts of terrorism directed at security officials charged with guarding some of the nation's most hardened crime kingpins.

Visiting Toulon prison in southern France, whose entrance was shot at with an AK-47 automatic rifle, Gerald Darmanin said he could not be sure if the attacks were linked to government efforts to clamp down on France's fast-growing drug trade.

But he said authorities were making life much harder for imprisoned gangsters, and the government would not shy away from tackling drug crime, which has boosted support for the far right.

"The Republic will not back down," he told reporters. "These are extremely serious crimes ... an attack on the public prison service, that is, a terrorist attack."

Years of record South American cocaine imports to Europe have transformed local drug markets, sparking a wave of violence.

Despite record cocaine seizures in France, gangs are reaping windfalls as they expand from traditional power bases in cities such as Marseille into smaller towns unused to drug violence.

Darmanin, who plans to create new high-security prisons to crack down on gangsters who run their empires from behind bars, said at least six prisons had been targeted.

Prison officers' union UFAP said vehicles were set on fire outside jails in Villepinte, Nanterre, Aix-Luynes, and Valence. In Nancy, a prison officer was threatened at home, while in Marseille, there was an attempted arson attack.

The National Anti-Terrorism Prosecutor's Office (PNAT) said it had taken charge of the probe into the attacks, which also targeted the National School of Prison Administration. The PNAT said officers from France's domestic intelligence agency DGSI would assist in the investigation.

Darmanin said it was unusual for PNAT, rather than specialised organised crime prosecutors, to take charge of the investigation, but it was justified due to the national scale of attacks against symbols of the state.

The letters "DDPF" – apparently an acronym for "French prisoners' rights" – were tagged on many of the attack sites, and police sources suggested it could be the work of a far-left militant group.

Darmanin said there had been "DDPF" groups on Telegram and Signal that had encouraged attacks against prisons, but "there hasn't been any claim of responsibility."

"I don't know who's behind this slogan, and I don't care because what I remember is not that a prison door was tagged, but that it was shot at by a Kalashnikov," he said.

Darmanin said the prison attacks reminded him of contracts given to gangsters to threaten, assault or kill rivals. (Reuters)