French police on Saturday arrested a man for apparently calling on a jihadi website for the decapitation of the editor of a magazine that published cartoons mocking Mohammed, a judicial source said.
The man was detained in the western city of La Rochelle for calling on the radical website for the head of satirical weekly Charlie Hebdo, which on Wednesday published cartoons of a naked Prophet.
"The essential thing is not to let him live in peace," the man allegedly wrote.
Police have opened a preliminary probe on charges of incitement to commit murder, the source said.
France's Muslim leaders on Friday urged militants not to defy a ban on protests over the cartoons, as a security alert closed the country's embassies across the Islamic world.
Interior Minister Manuel Valls has made it clear he will not sanction any demonstrations this weekend on the grounds they will inevitably represent a threat to public order.
The cartoons were published as often violent -- and sometimes deadly -- protests continued across the world against an anti-Islam film made in the US that enraged many Muslims.
A rowdy protest at the film close to the US embassy in Paris last weekend led to 150 arrests and there have been calls on social networks for another demonstration in central Paris on Saturday.