Several training grenades were thrown into the courtyard of a mosque in the French city of Le Mans.
One exploded, but no injuries were reported.
Police cordoned off the building. There have been no reports of arrests, Euronews reported.
A “criminal” explosion occurred early on Thursday morning at a kebab shop near a mosque in the eastern French town of Villefranche-sur-Saone, officials said, but left no casualties.
“It is a criminal act,” a local official told Agence France-Presse news agency, adding that a police investigation has been opened. No link was suggested with the Paris attack a day earlier.
French Interior Minister Bernard Cazeneuve in a televised press conference said the threat in France remains “very serious” as police continue the hunt for Wednesday’s killers but warned: “We shall not tolerate any threat against a place of religion or hostile demonstration against the French people because of their origin or their religion.”