PARIS — The investigation into the Paris terrorist attacks unfurled across Europe yesterday as French authorities sought a possible eighth assailant who might have fled after the three terrifying hours on Friday night in which at least 129 people were killed and 352 were injured, including 99 who remain in serious condition.

In the eastern Paris suburb of Montreuil, the authorities found three Kalashnikov rifles — the kind used in the attacks — in an abandoned black Seat Leon that was used as a getaway car for the attackers at restaurants in central Paris.

A French official who was briefed about the investigation but was not authorised to speak publicly said the authorities were looking for someone from the Paris region who might have participated in the attacks. The authorities had initially said there were eight attackers, but on Saturday night said that only seven attackers had died — six by blowing themselves up and one in a police shootout.

Investigators were hunting for more information on one attacker, Ismael Omar Mostefai, 29, a French citizen who had been living in Chartres, 97km south-west of Paris, and who died at the Bataclan concert hall on Friday night.

French officials were also coordinating closely with Belgian authorities, who made a series of arrests in a Muslim-majority neighbourhood outside Brussels on Saturday. One man they detained was linked to a rented Volkswagen Polo that had been used by the three terrorists who killed 89 people at the Bataclan concert hall.

Two of the attackers who died were Frenchmen who had lived in Brussels, Belgian prosecutors said yesterday.

Reports from Serbia yesterday said the authorities there had identified the holder of a Syrian passport found near one of the attackers in Paris. Responding to requests from French officials, Greece and Serbia confirmed that the holder of the passport had passed through their countries last month along with tens of thousands of migrants fleeing Syria, Iraq and Afghanistan.

Fundamental questions remained: How the terrorists, who acted in three synchronised teams, managed to pull off the deadliest terrorist attack in Western Europe since 2004, and whether they received direction from Islamic State leaders in Iraq and Syria, who until now had never taken responsibility for such a large-scale attack in the West. But the carefully coordinated attacks now appear increasingly likely to have drawn from people from several nations and to have involved extensive planning as well as sophisticated weapons.

Mostefai was publicly identified in a Facebook post by Chartres mayor Jean-Pierre Gorges. Mostefai, who was one of three hostage-takers at the Bataclan, was identified based on a print from his severed finger.

Paris prosecutor Francois Molinssaid Mostefai was arrested in connection with a series of low-level crimes from 2004 to 2010 and had been under surveillance since 2010, having been listed in a French security services database of people who have fallen under the influence of extremist Islamist beliefs.

Six of his relatives were detained for questioning yesterday.

As the investigation proceeded, US President Barack Obama said in Turkey, where he and other leaders of the Group of 20 nations gathered for a summit meeting, that the “skies have been darkened by the horrific attacks” in Paris and pledged that America would support France, its oldest ally.

“We stand in solidarity with them in hunting down the perpetrators of this crime and bringing them to justice.” AGENCIES