Several Kalashnikovs have been found in an abandoned car believed to have been used by some of the Paris attackers, French judicial sources say.
The black Seat car was found in the eastern Paris suburb of Montreuil on Sunday and suggests some of the attackers got away.
Earlier, the first of the seven dead attackers was named as Ismail Mostefai.
Six people close to him are in custody.
France is in three days of mourning for the 129 people killed in the attacks.
A special service for the families of the victims, the 350 people who were wounded, and the other survivors will be held at Paris's Notre Dame Cathedral later on Sunday.
Friday's attacks, claimed by Islamic State (IS) militants, hit a concert hall, a major stadium, restaurants and bars in the French capital.
Prime Minister Manuel Valls has said France will continue with air strikes against IS in Syria, and described the group as a very well-organised enemy.
President Francois Hollande has cancelled his plans to attend the G20 in Turkey and is holding meetings with various political leaders to discuss the crisis.
The black Seat car, found in Montreuil, is believed to have been used by gunmen who opened fire at people in restaurants on Friday night, police say.
Several AK47 rifles were found in the car, French media quotes judicial sources as saying.
It appears to confirm the theory that some of the gunmen managed to flee from the scene after the attacks, the BBC's Hugh Schofield reports from Paris.
These men may then have driven north in another car to Belgium, he adds.
Three men were arrested in Belgium on Saturday in connection with the attacks.
Another car, a Volkswagen Polo, with Belgian number plates was found near the Bataclan concert venue, where nearly 90 people were killed.
Paris chief prosecutor Francois Molins said that car had been rented by a French national living in Belgium.
“We can say at this stage of the investigation there were probably three co-ordinated teams of terrorists behind this barbaric act,” Mr Molins said.
“We have to find out where they came from… and how they were financed.”
A Syrian passport, found near the body of one of the attackers at the Stade de France, had been used to travel through the Greek island of Leros last month, Greek officials have confirmed.
Serbia says the holder of that passport had also crossed its border from Macedonia and sought asylum at one of its registration centres.
No direct link has yet been made with the holder of the passport and the attackers.
Mostefai was reportedly identified after investigators found a severed finger at the scene of the worst atrocity, the Bataclan concert hall where more than 80 people died.
He came from the town of Courcouronnes, 25km (15 miles) south of Paris. He lived in the city of Chartres 100km south-west of Paris until 2012, according to the local MP and deputy mayor Jean-Pierre Gorges.
He is said to have regularly attended the mosque in Luce, close to Chartres.
La Belle Equipe, 92 rue de Charonne, 11th district – 19 dead in gun attacks
La Casa Nostra restaurant, 92 rue de la Fontaine au Roi, 11th district – five dead in gun attacks
Stade de France, St Denis, just north of Paris – explosions heard outside venue, three attackers and bystander dead
Bataclan concert venue, 50 Boulevard Voltaire, 11th district – 89 dead when stormed by gunmen
Mostefai had a history of petty crime but was never jailed. The security services deemed him to have been radicalised in 2010 but he was never implicated in a counter-terrorism investigation.
Police are said to be trying to find out whether he travelled to Syria in 2014.
His father, brother and sister-in-law are among six people close to Mostefai who have reportedly been taken into police custody.
“It's crazy, insane. I was in Paris myself last night, I saw what a mess it was,” Mostefai's older brother told AFP before being detained after voluntarily attending a police station on Saturday.
Mostefai's brother said he had not had contact with him for several years following family disputes, but said he was surprised to hear he had been radicalised.
He was one of six children in the family and had travelled to Algeria with his family and young daughter, the brother said.
French President Francois Hollande has imposed a state of emergency after the worst peacetime attack in France since World War Two. It is also the deadliest in Europe since the 2004 Madrid bombings.
Islamic State said it carried out the attacks on “carefully chosen targets” and were a response to France's involvement in the air strikes on IS militants in Syria and Iraq.
President Hollande said France had been “attacked in a cowardly shameful and violent way” and vowed to be “merciless” in its response to IS militants.