France’s national terrorism office has launched an investigation into a wave of apparently coordinated attacks at multiple prisons across the country believed to be linked to a government clampdown on drug traffickers.

Gunmen with automatic weapons opened fire on the entrance to Toulon prison in southern France in the early hours of Tuesday, while in recent days cars have been set alight outside four other jails, and in Marseille a residential building housing prison guards was attacked.

The attacks came as the French parliament prepares to approve a new law increasing the power of police investigating drug dealers, toughening prison conditions for convicted traffickers and creating a new prosecutors’ office responsible for investigating organised crime.

Soaring cocaine imports from South America to Europe have sparked drug-linked violence in France where seizures of the drug are at a historic high, police say. The drug gangs traditionally based in cities like Marseille have expanded into smaller regional towns unused to drug violence.

The justice minister, Gérald Darmanin, was due to visit Toulon prison on Tuesday afternoon in a show of solidarity with staff. Darmanin said he was determined to stamp out drug kingpins’ capacity to operate from behind bars and has ordered the building of two new high-security jails to hold more than 700 prisoners.

“Attempts have been made to intimidate staff in several prisons ranging from burning vehicles to firing automatic weapons. The French Republic is facing up to the problem of drug trafficking and taking measures that will massively disrupt the criminal networks,” Darmanin wrote on X.

He added: “The Republic is confronted with drug trafficking and is taking measures that will deeply disturb criminal networks. It is being challenged and will be firm and courageous.”

Prisons in Marseille, Aix-en-Provence, Valence, Nîmes, Luynes, Villepinte and Nanterre were also targeted. Staff unions said burnt vehicles had been found in prison car parks for several days in the runup to what appeared to be Monday night’s coordinated assault. Cars have also been set alight outside the National School of Prison Administration.

The legislation before the French parliament would allow prisons to hold convicted drug dealers in isolation, deprive them of collective walks and access to family life units, tap their phones and limit calls. Darmanin has also proposed giving the justice minister the power to decide whether solitary confinement orders – which must currently be renewed every three months – can be applied for up to four years, and applied not only to convicted drug traffickers but also those awaiting trial.

The appointment of the National Anti-Terrorism Prosecutor’s Office (PNAT) to oversee the investigation, as opposed to the organised crime unit, suggests police believe the attacks may be the work of a militant group. PNAT said it would be working with the country’s interior intelligence agency.

The interior minister, Bruno Retailleau, said the attacks were “unacceptable” and ordered increased police protection of prisons and staff.

In February – as he announced record cocaine seizures of 47 tonnes in the first 11 months of last year, more than double that seized in 2023 – Retailleau said France had been hit by a “white tsunami” that had rewritten the rules of the criminal landscape.