Three teams of attackers were involved in the Paris attack in which 129 people were killed and more than 350 wounded, France's 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.
Mr 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 may have 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.
A Syrian passport was found next to the body of one of three suicide bombers who struck near the Stade de France stadium during Friday's game, Mr Molins said.
A Greek minister says the passport belonged to a Syrian refugee who passed through the island of Leros. An Egyptian passport has also been linked to the attacks.
French President Francois Hollande 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.
The violence began soon after 21:00 (20:00 GMT) as people were enjoying a Friday night out in the French capital.
A gunman opened fire on Le Carillon bar in the rue Alibert, near the Place de la Republique, before heading across the road to Le Petit Cambodge (Little Cambodia), killing 15 people.
"We heard the sound of guns, 30-second bursts. It was endless," resident Pierre Montfort said.
A few streets away, diners sitting on the terrace of La Casa Nostra pizzeria in rue de la Fontaine au Roi, were also fired on, with the loss of five lives.
Mr Molins said 19 people were killed at the Belle Equipe bar, while the toll from the attack on the Bataclan concert hall stood at 89.
At around the same time, on the northern outskirts of Paris, 80,000 people who had gathered to watch France play Germany at the Stade de France heard three explosions outside the stadium.
President Hollande was among the spectators and was whisked away after the first blast.
Investigators found the bodies of three suicide bombers around the Stade de France, Mr Molins said.