France has foiled "a terrorist act against French military facilities", and four suspects are in custody of the country's intelligence services.
Interior Minister Bernard Cazeneuve said the suspects, aged 16 to 23 and including a former navy member, were arrested at dawn in different parts of the country.
He said there's no link had been established between the foiled assault and two blasts on Tuesday at a petrochemical plant near Marseille.
French news agency AFP quotes an anonymous source by saying the suspects had been planning to film the decapitation of a member of the military.
The news of the arrests followed a statement from President Francois Hollande, who said attacks had been thwarted in recent days.