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.
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.
He said all seven militants had used Kalashnikov assault rifles and the same type of explosive vests.