A French police officer was injured on Saturday when a blazing car exploded in the car park of a synagogue in the town of La Grande-Motte.
Police said they were treating the incident as attempted arson and several politicians as well as Jewish organisations denounced it as an antisemitic attack.
BFM TV said the anti-terrorism prosecutor's office would be in charge of the case.
Prime Minister Gabriel Attal said the authorities would be ruthless with antisemitism.
"The person (attacker) set fire to several entry doors to the synagogue and several cars," Attal said after visiting the synagogue, adding an "absolute tragedy" had been narrowly averted after firefighters and police arrived quickly at the scene.
French government officials have warned security at Jewish institutions will be ramped up following the incident.
France has seen a surge in antisemitism following the Hamas attacks on Israel on October. 7 and Israel's retaliatory assault on Gaza which has left thousands dead and hundreds still held captive by Hamas.
Local media said two cars, one of which contained at least one gas bottle, had been set on fire in the synagogue's parking area, at about 8:30 a.m.
"Exploding a gas bottle in a car in front of the Grande Motte synagogue at the expected time of arrival of the faithful: it's not just attacking a place of worship, it's an attempt to kill Jews," Yonathan Arfi, who leads the CRIF, an umbrella organisation of French Jewish groups, said on X.
William Maury, of police union Alliance Police Nationale, told BFM TV the injured police officer's life was not in danger. Police confirmed the attempted arson but declined to give more details.
Interior Minister Gerald Darmanin said police were looking for a suspect. "I want to assure our fellow Jewish citizens and the city (of La Grande-Motte) of all my support and say that at the request of the President of the Republic @EmmanuelMacron, all means are being mobilised to find the author (of the attack)," Darmanin said on X.
Darmanin said police protection of synagogues and Jewish schools and shops would be strengthened across France.
