Security around Jewish sites was tightened following the early Saturday blast outside the Beth Yaacov synagogue in the seaside resort of La Grande Motte, near the city of Montpellier.
Two cars outside the synagogue burst into flames after a gas canister likely exploded inside one of the vehicles, police said. The blast wounded a police officer.
Prime Minister Gabriel Attal said France's national anti-terror prosecutors had been tasked with probing the incident.
"La Grande Motte's synagogue was the target of an attack this morning," Attal said in a post on X. "An anti-Semitic act. Once again, our Jewish fellow citizens are being targeted."
Earlier, Interior Minister Gerald Darmanin called the incident "an obviously criminal act".
He said that "all means are being deployed to find the perpetrator".
The police presence outside Jewish sites in France would be increased following the explosion, the minister added. Darmanin and Attal were to travel to the site of the explosion on Saturday.
La Motte's mayor, Stephan Rossignol, said that CCTV had picked up images of an individual setting fire to the cars.
The blast occurred during Shabbat, the Jewish day of rest that runs from sunset Friday to sunset Saturday and often when many attend synagogue services.
There was, however, no religious service ongoing at the time of the incident, a police source said.
Comment: That's notable.
Two doors of the synagogue were damaged in the blast.
There was no immediate information about the gravity of the police officer's injuries.
The town near Montpellier has about 8,500 permanent residents but the population swells during the summer tourism season.
The explosion comes amid a heightened state of alert in France and other European countries because of the war in Gaza.
Darmanin said this month that the government had counted 887 anti-Semitic acts in France in the first half of 2024, nearly three times as many as in the same period in 2023.
Comment: Criticising Israel's genocide of Gazans, or supporting Palestine's legal right to defend itself, has been deemed an act of anti-semitism - despite DNA studies showing that Palestinians are Semites - and so this count is extremely dubious: Algerian footballer for France's Nice club convicted over Gaza post
France is home to the biggest Jewish population outside Israel and the United States, and also to the largest Muslim community in the European Union.
The Representative Council of Jewish Institutions in France (CRIF) called the explosion "an attempt to kill Jews".
The use of a gas canister "in a car at a time when worshippers are expected to arrive at the synagogue is not simply a criminal act", CRIF president Yonathan Arfi told AFP. "This shows an intention to kill."
Police have locked down the area around the synagogue.
Comment: It remains to be seen just exactly happened here, but, across the West, there appears to have been a spike in seemingly unstable individuals attacking various groups in society; Judaism, and Zionism, do not appear to be anymore a target than other groups: