A French man believed directly involved in Friday's attacks in Paris is on the run and the subject of a manhunt, French security officials say.

The man, one of three brothers believed involved in the killings in central Paris, rented a black Volkswagen Polo used by a group of hostage-takers that left at least 89 people dead inside the Bataclan concert hall, one official said.

One other police official said the manhunt is believed to involve at least one suspect. One of the suspect's brothers has been arrested in Belgium, and another brother died in the attack, the first official said.

As Paris on Sunday mourned the attacks' 129 victims at a special mass at Notre Dame Cathedral, French police identified one of the gunmen involved in the assault.

Omar Ismail Mostefai, a 29-year-old Paris native, was named as one of the seven assailants, all of whom were wearing suicide bomb vests packed with explosives, who died during Friday’s rampage. His detached finger was found overnight at the Bataclan concert hall, the scene of the bloodiest attack.

French media described him as a French-born man of Algerian descent. Paris prosecutor François Molins said he had a security file for radicalization, adding that he had a criminal record but had never spent time in jail.

A Belgian official says seven people have been detained in Belgium in connection to the Paris attacks. The official said two of the seven attackers who died in Paris on Friday night were Frenchmen who had been living in Brussels.

A judicial source said Mostefai's father and brother had been taken in for questioning, along with other people believed to be close to him.

Also on Sunday, it was reported that a Seat car suspected to be linked to Friday's massacre had been found by police in Montreuil, a suburb nearly 4 miles east of the French capital. Several automatic weapons, of the sort used in the attacks, were found in the abandoned vehicle, a judicial source said.

French authorities believe the coordinated attacks — which targeted a concert hall, and several bars and restaurants crowded with Friday night revelers — were planned abroad by the Islamic State in Iraq and the Levant (ISIL).

ISIL has claimed responsibility for the assault. In a statement Saturday, the group said its fighters, armed with suicide-bomb belts and machine guns, carried out the attacks at locations that were carefully studied. The attack was designed to show France that it would remain a top target for the group as long as it continues its current polices, the statement continued. Alongside the 129 known to have died, hundreds more were injured.

The leaders of Hamas, Hezbollah and Islamic Jihad all issued statements denouncing the attacks, Deutsche Welle reported.

French Muslim groups have denounced the assault and expressed concern that it could prompt a backlash against members of the country's Islamic community.

The police investigation into Friday’s massacres continues amid heightened tension and high security in Paris. France has put thousands of soldiers onto the streets to reinforce police and other security personnel.

Meanwhile a G-20 summit in Turkey has taken on more urgency. Turkish President Tayyip Erdogan on Sunday urged the gathered world leaders to prioritize the fight against ISIL, saying the Paris attacks showed the time for words is over.

French President François Hollande pulled out of the summit to stay in Paris. On Saturday, he vowed — using the Arabic acronym for ISIL — that France would be “merciless” in its efforts against “these barbarians from Daesh."

The Investigation

Obama on Sunday pledged solidarity with France and said the U.S. would “redouble” its fight against ISIL.

It is believed that the attackers worked in three coordinated teams, and that the seven who blew themselves up wore identical explosives vests.

Throughout the weekend, investigators across Europe worked to identify the attackers and hunt for any accomplices.

In Belgium, police arrested several people over alleged links to the attacks. Witnesses said some of the attackers arrived in a car carrying Belgian plates.

German police arrested a man on Nov. 5 after automatic weapons, hand guns and explosives were found in his vehicle during a routine check on a motorway.

Horst Seehofer, Bavaria's state premier, said there was reason to believe he had links to the attackers. Refugees and borders

Greek authorities have also confirmed that a man who died in the attacks with a Syrian passport found next to him had registered as a refugee in October.

Serbian police say the owner of a passport found near a suicide bomber in Paris entered the country on Oct. 7 from Macedonia, part of a wave of asylum-seekers crossing the Balkans toward Western Europe.

Police said in a statement Sunday that the man, identified only as A.A., formally requested asylum in Serbia. The statement says it's the same passport holder registered as entering Greece on Oct. 3.

If confirmed, any link between the attacks to people who entered Europe as part of a flow of refugees could have far-reaching political consequences.

Europe is already divided over how to handle the arrival of hundreds of thousands of refugees and other migrants from war in Syria, Iraq and Libya.

Marie Le Pen, the leader of France's far-right National Front party, has called for a tightening of the country's borders.

And in a sign of potential divisions ahead, Poland said that the attacks in Paris meant it could not now take its share of migrants under a European Union relocation plan. The victims

As French authorities begin to identify those involved in the attack, more details of the innocent victims of the assault are becoming known. In a nod to Paris’ cosmopolitan standing, the victims include people from around the world — a U.S. citizen, one Swede, one Briton, two Belgians, two Romanians and two Mexicans are among those known to have died.

An American college student, Nohemi Gonzalez, 23, was among those killed. She was enrolled at California State University at Long Beach, a spokesman for the university said. A senior, she was studying for a semester at the Strate College of Design in France, according to school authorities.

Gonzalez was one of 19 people killed at La Belle Equipe, a bistro, where nine others were critically wounded.

Nick Alexander, a member of the entourage of California-based rock band Eagles of Death Metal, was identified in a statement from his family as one of at least 89 people who died when gunmen stormed the Bataclan music hall in the midst of Friday night's show.

Their lives, along with that of the 127 other known victims of Friday’s attacks. will be remembered at a special service planned at Notre Dame Cathedral later Sunday. Families of the victims and survivors are expected to attend the mass, during which the famed cathedral will toll its bells in a special homage to the dead.

Originally published by Al Jazeera America