The department of the French prosecutor's office, which deals with anti-terrorism, has opened an investigation into the explosion in front of a synagogue in the south of France, reported DPA, quoted by BTA.
The perpetrator is still being sought, Prime Minister Gabriel Attal said.
Two cars were initially set on fire outside the synagogue in the seaside resort of La Grand Motte near Montpellier in southern France.
A gas bottle exploded in one of the two cars, a gendarmerie spokesman said. One policeman was injured in the incident, there were no other injured in the building.
Two of the synagogue's doors also caught fire, but it is unclear whether this happened before or after the explosion.
French Interior Minister Gérald Darmanen ordered an immediate increase in the presence of security forces outside Jewish temples. He wrote in "X" that it was "an obvious criminal attempt at arson" and expressed his full support for the Jewish community.
Atal uploaded a post on "X" in which he stated that it was an anti-Semitic act. "Our dear Jewish citizens have been targeted again," it said.
Saturday is the day of the Jewish Sabbath, and traditionally people go to service on that day.
Yonathan Arfi, chairman of the umbrella organization of Jewish organizations in France, said the explosion occurred as worshipers were expected to arrive at the synagogue.
"This was not just an attempted attack on a temple, it was an attempt to kill Jews," he wrote.
Atal and Darmanen are expected to arrive at the scene of the attack.