Three teams carried out the attacks in the French capital which killed 129 people and left more than 350 wounded, the Paris chief prosecutor says.
“We have to find out where they came from… and how they were financed,” Francois Molins told reporters.
He said seven attackers had been killed, and that all had been heavily armed and wearing explosive belts.
Friday’s attacks, claimed by Islamic State militants, hit a concert hall, a major stadium, restaurants and bars.
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.
Molins confirmed that one of the dead attackers had been identified as a 29-year-old Frenchman who had a criminal record, but had never spent time in jail.
Omar Ismaïl Mostefai was identified after his finger was found at the Bataclan concert hall and matched fingerprints the police had on file, AFP reported.
Mostefai came from the town of Courcouronnes, 25km (15 miles) south of Paris. He had been identified by the security services as having been radicalised but had never been implicated in a counter-terrorism investigation, reports the BBC.
Investigators are trying to find out whether he travelled to Syria in 2014, judicial sources told AFP.
French police have taken Mostefai’s father and brother into custody and searched their homes.
Mostefai’s older brother attended a police station voluntarily.
He said he had not had contact with his younger brother for several years.
Molins also said the arrests of three men in Belgium on Saturday were linked to the attacks.
Belgian Prime Minister Charles Michel said investigators were trying to establish whether one of the suspects picked up near Brussels might have been in Paris on Friday evening.
Speaking in Paris on Saturday evening, Molins told reporters: “We can say at this stage of the investigation there were probably three co-ordinated teams of terrorists behind this barbaric act.”
Molins said all seven militants had used Kalashnikov assault rifles and the same type of explosive vests.
Molins also gave details about the state of the investigation, which he said was at a very early stage.
He said police were focusing on two vehicles. One is a black Seat used by gunmen at two of the attacks, and still untraced.
The other is a black Volkswagen Polo with Belgian registration plates found at the concert venue that was targeted.
He said this had been rented by a Frenchman living in Belgium.
He was identified while driving another vehicle in a spot check by police on Saturday morning as he crossed into Belgium with two passengers.
The BBC’s Hugh Schofield in Paris says investigators are working on the theory that these three may be another team of attackers who managed to flee the scene.
The Greek authorities say two people under investigation by the French police had registered in Greece as Syrian refugees. A Syrian passport was found near the body of one the attackers at the Stade de France.
An Egyptian passport has also been linked to the attacks.
