Three teams of attackers were involved in the assault on Paris, in which 129 people have been killed and more than 350 injured, the Paris 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.
The attacks on Friday night hit a concert hall, a major sports stadium, restaurants and bars.
Mr Molins also said the arrests of three men in Belgium on Saturday were linked to the attacks.
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Meanwhile Belgian Prime Minister Charles Michel announced that one of the suspects picked up near Brussels had been in Paris on Friday evening.
Speaking in Paris on Saturday evening, Mr 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.»
He also confirmed that one of the dead attackers had been identified as a 30-year-old Frenchman who had a criminal record but had never spent time in jail.
The man came from the town of Courcouronnes, 25km (15 miles) west of Paris. He had been identified by the security services as having been radicalised but had never been implicated in a counter-terrorism investigation.
Mr Molins said all seven militants had used Kalashnikov assault rifles and the same type of explosive vests.
He 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 was 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 to a Frenchman living in Belgium who was identified in a spot check by police on Friday morning as he drove across the Belgian border with two others.
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.