Paris: French anti-terror police have arrested six men in the cities of Strasbourg and Marseille, security sources told AFP on Monday.
Four men were arrested in eastern Strasbourg overnight on Saturday to Sunday, with another two detained in southern Marseille the same evening, several sources close to the case told AFP on condition of anonymity.
"Serious information made these arrests necessary," one source told AFP, asking not to be named because he was not authorised to speak on the case.
Interior Minister Bernard Cazeneuve is set to give more details about the arrests later in the day.
Strasbourg has been on high alert ahead of the opening of its Christmas market, with local officials warning it could be suspended or cancelled if there were serious threats.
France remains in a state of emergency a year since attacks by Islamic State jihadists on Paris which left 130 people dead.