According to French chief prosecutor Francois Molins, three teams of attackers were involved in the Paris attack in which 129 people were killed and more than 350 wounded.
“We have to find out where they came from… and how they were financed,” he told reporters.
Francois Molins said seven attackers had been killed, and that all had been heavily armed and wearing explosive belts.
Last night’s attacks, claimed by ISIS, hit a concert hall, a major stadium, restaurants and bars.
Francois Molins also said the arrests of three men in Belgium on November 14 were linked to the attacks.
Belgian PM 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 November 14, Francois 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, 15 miles west of Paris. He had been identified by the security services as having been radicalized but had never been implicated in a counter-terrorism investigation.
Francois 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.
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.
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, Francois 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.
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 local time as people were enjoying a Friday night out in Paris.
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.
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.
Frnacois 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 Francois 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, Francois Molins said.
The 1,500-seat Bataclan concert hall suffered the worst of last night’s attacks. Gunmen opened fire on a sell-out gig by rock group Eagles of Death Metal, killing 89 people.
Within an hour, security forces had stormed the concert hall and all four attackers there were dead. Three had blown themselves up and a fourth was shot dead by police.
ISIS released a statement on November 14 saying “eight brothers wearing explosive belts and carrying assault rifles” had carried out the attacks on “carefully chosen” targets, and were a response to France’s involvement in the air strikes on ISIS militants in Syria and Iraq.
Shortly before, President Francois Hollande said France had been “attacked in a cowardly shameful and violent way”.
“So France will be merciless in its response to the Islamic State militants,” he said, vowing to “use all means within the law.. on every battleground here and abroad together with our allies”.
Many official buildings as well as Disneyland Paris have been closed, sports events have been cancelled and large gatherings have been banned for the next five days.