The attackers at the Bataclan concert hall evoked Syria and Iraq during their killing spree in Paris, a French prosecutor said.
Francois Molins said three teams in identical explosives vests seem to have co-ordinated the "act of barbarism" that left 129 people dead and 352 injured across the French capital.
He said the French authorities had a security file on one of the Bataclan killers because of his Islamist radicalisation and he had a criminal record, but had never spent time in jail.
Mr Molins also confirmed that one of the hostage-takers involved in the siege was a French national.
Meanwhile, three people, including a French national, were arrested at the Belgian border, There were also police raids in the Molenbeek area of Brussels.
Three of the eight suspects lived in the city, according to reports in Belgian media.
An anti-terrorist investigation in Belgium will focus on a car that had been hired in the country and was found near the Bataclan concert hall.
French broadcaster BFMTV said that in addition to a Syrian passport found at the scene of a deadly stadium attack in the north of the city, an Egyptian passport was found close to the body of one of the assailants.
The Syrian was not known to French intelligence services, said Mr Molins.
A Greek minister has said that the Syrian passport belonged to someone who had got into the EU via Greece in early October.
Greek government sources told Reuters a second suspect was also very likely to have passed through the country.
:: Running For Their Lives From Concert 'Carnage'
One witness of the Bataclan attack - one of six co-ordinated assaults on Friday night - told French radio they heard an attacker shouting "Allahu Akbar", or "God is great", as the killing spree started.
Another man, Ludovic Mintchop said he was walking down Boulevard Richard Lenoire, south of the attacks at a restaurant and bar in Paris on Friday night, when he saw a black, German-made sedan screeching to a stop in front of him.
Two men emerged from the car with Kalashnikovs before shooting two people on rental bikes.
Islamic State has claimed responsibility for the near-simultaneous attacks and has warned that France would remain at the "top of the list of targets" over its airstrikes on IS territory in Syria and Iraq.
It said in an online statement that eight militants armed with explosive belts and guns chose targets "in the capital of adultery and vice".
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Supporters of IS have taken to social media using the hashtag "Paris is burning".
Military have been deployed to boost security across Paris, and tourist attractions such as the Eiffel tower and the Louvre Museum have been shut until further notice amid fears of further violence.
French President Francois Hollande earlier the assaults were an "act of war" by IS.
In Germany, officials have said a 51-year-old man arrested with weapons in his car last week may be linked to the Paris attacks.
:: Terror In Paris: How The Attacks Unfolded
Firearms, explosives and hand grenades were found in the vehicle near the German-Austrian border - but Bavarian state police would not confirm reports that the man appeared to be en route to Paris when he was held.
:: The Foreign Office says those concerned about British nationals caught up in the attacks should call 020 7008 0000.
:: Ireland's Department of Foreign Affairs says anyone concerned about Irish nationals caught up in the attacks should call 01 408 2000.