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.
President Francois Hollande had described Friday's attacks in Paris as an act of war – and promised that France's reaction would be pitiless.
Ten fighter jets operating out of French bases in Jordan and the UAE dropped 20 guided bombs on a command centre, recruitment centre for jihadists, a munitions depot and a training camp for fighters, the ministry said.
The attack was carried out in co-ordination with US forces.
Panic in Paris
French Interior Minister Bernard Cazeneuve said Friday night's attacks in Paris had been prepared "by a group of individuals based in Belgium" who had "benefited from accomplices in France".
The attackers targeted bars and restaurants, a concert hall and the Stade de France, the country's main sports stadium.
France is marking three days of national mourning. On Sunday, a memorial service was held at Notre Dame cathedral.
Meanwhile panic broke out at the Place de la Republique, where hundreds of people had gathered to honour the victims.
Crowds ran over flowers and candles. Police – who cleared the square – later said people may have mistaken the sound of firecrackers for gunfire.
French police appealed for information about Salah Abdelslam but warned people not to approach him. Unnamed officials said he was one of three brothers linked to Friday's attack.
Reports say Abdeslam had already been identified as the renter of a VW Polo found at the Bataclan concert hall, where 89 people were killed, when police near the Belgian border stopped him and two others as they travelled in another vehicle on Saturday morning.
But the officers let him go after checking his ID, media reported, quoting French police and security sources.
A Seat car found in Montreuil is believed to have been used by gunmen who opened fire on people in bars and restaurants on Friday, police say. A number of AK47 rifles were found in the car, French media quote judicial sources as saying.
Both the Seat and the VW Polo were rented in Belgium.
One of the Paris attackers lived in Brussels and another in the nearby suburb of Molenbeek, Belgian prosecutors said on Sunday, without naming either.
A total of seven men had been arrested in Molenbeek, they added. Not all are being held in direct connection with the Paris attacks. A brother of Salah Abdelslam was said to be among them, while another brother is reported to be one of the seven dead attackers.
The only dead attacker to be named so far is a 29-year-old Frenchman, Ismail Omar Mostefai. He had a criminal record and had been flagged up as a possible Islamist extremist by French intelligence.