PARIS (AFP) - Paris prosecutors said their investigation would allow them to see if any "accomplices or co-authors are on the loose" after attacks on Friday (Nov 13) that left more than 120 dead.

An initial investigation has been opened for "killings in relation to a terrorist enterprise", said chief prosecutor Francois Molins, adding there were at least seven attackers in total.

Four men who attacked a concert hall in Paris on Friday killing around 100 people were themselves killed when police stormed the building, including three who activated explosives belts, several sources said.

"Three of them blew themselves up and a fourth, who was also wearing a belt, was hit by police fire and blew up as he fell," one source said.

One of the assailants in Paris mentioned France's intervention in Syria's war to justify the attacks, said a witness who was at a concert venue where some 100 people were killed.

"I clearly heard them say 'It's the fault of (French President Francois) Hollande, it's the fault of your president, he should not have intervened in Syria'. They also spoke about Iraq," said Mr Pierre Janaszak, a radio presenter.