Vehicles were set alight outside several French prisons, and one jail was hit by gunfire from an automatic weapon, in a wave of overnight attacks, reports BBC News.
Justice minister Gérald Darmanin said the jails had faced "intimidation attempts" and linked the attacks to the government's crackdown on drug trafficking.
Seven establishments were targeted, according to Le Parisien newspaper: in Toulon, Aix-En-Provence, Marseille, Valence and Nîmes in southern France, and in Villepinte and Nanterre, near Paris.
France's national anti-terrorism prosecutor's office said it was investigating.
In a post on X, Darmanin said he was travelling to support affected officers at the prison in Toulon, which was targeted with gunfire.
Without directly attributing blame for the attacks, he said the French government was "facing up to the problem of drug trafficking" and taking measures that would "profoundly disrupt" criminal networks.
Interior minister Bruno Retailleau said the government's response must be "relentless".
"Those who attack prisons and officers deserve to be locked up in those prisons and monitored by those officers," he posted on X.
He added that he had instructed police to immediately strengthen security at prison facilities.
Read more of this report from BBC News.