Police have issued a photograph of a French national wanted in connection with Friday's deadly attacks in Paris that left 129 people dead.
The man, named as Salah Abdeslam, 26, is described as dangerous.
Reports say he had already been identified as the renter of a car used in the attack when he and two others were stopped by police near the Belgian border.
The officers apparently let him go after checking his ID.
Seven attackers, two of whom had lived in Belgium, died during a series of assaults in the city, officials said.
Late on Sunday, French aircraft struck Raqqa in Syria - the stronghold of Islamic State (IS), the militant group that has claimed it was behind the Paris attacks.