PARIS — French authorities were racing Sunday to hunt down any potential accomplices to the wave of terror attacks unleashed in Paris as the investigation widened beyond this nation’s borders.

A French man believed to be directly involved in Friday's massacre in Paris is on the run and the subject of an international manhunt, French security officials said Sunday evening.

Investigators said the man rented a Belgian-registered black Volkswagen Polo, which was allegedly used and abandoned by the hostage-takers who killed at least 89 people inside a Paris concert hall.

He was identified by officials as Salah Abdeslam, 26, from Brussels.

[AppelàTémoin] La #PJ recherche 1 individu susceptible d'être impliqué ds les attentats du 13/11/2015 #ParisAttacks pic.twitter.com/Gpr4MY1I53 — Police Nationale (@PNationale) November 15, 2015

Abdeslam is allegedly the brother of another suspect currently in custody and being questioned — and of one of the deceased attackers, officials said.

French officials were working with authorities in Belgium, Spain and Serbia in an attempt to shed more light on the attack, which ISIS claimed responsibility for and which French President Francois Hollande described as an "act of war."

Less than two days after the attacks Sunday, French warplanes conducted raids in Syria, targeting ISIS’ stronghold in Raqqa, the defense ministry said. Reuters reported that the operation was France’s biggest strike against ISIS in Syria to date.

"The raid ... including 10 fighter jets, was launched simultaneously from the United Arab Emirates and Jordan. Twenty bombs were dropped," the ministry said in a statement.

The airstrikes, which were carried out in coordination with the U.S., hit a command post, a jihadist recruitment center, a munitions depot and a militant training camp, the statement said.

Three separate teams of terrorists armed with Kalashnikovs and identical explosives vests laid coordinated siege to Paris on Friday night, according to the Paris prosecutor. More than 100 people were killed at six locations and at least 350 were injured.

And the FBI has sent a "small contingent" of counter-terrorism investigators to Paris to augment its legal affairs representatives already there, the bureau said.

French Interior Minister Bernard Cazeneuve said Sunday that he would use the state of emergency declared Friday night to "act more rapidly" in the "dissolution of mosques where hate is preached."

While officials have released a timeline of the attacks, authorities have offered little information on the attackers' identities.

Related: Get the Latest Updates on Paris Attacks

Paris Prosecutor Francois Molins said seven terrorists died in the attack on Friday. Officials initially said there were eight attackers — as did ISIS. It seems now Abdeslam is believed to be the eighth attacker.

Among the seven dead attackers was a French national, Omar Ismael Mostefai, a French judicial official said. He lived in Chartres, about 60 miles from Paris, at least until 2012, local lawmaker Jean-Pierre Gorge wrote on Facebook. The Associated Press reported that Mostefai, a suicide bomber who died in the assault on the Bataclan concert hall,had known ties to Islamic radicalism.

Mostefai’s brother and father were taken into custody, a former French official said Saturday.

A French prosecutor also said officials have identified two more assailants, whose names were not released to NBC News — a 20-year-old who was part of the attack on the Stade de France and a 31-year-old who was part of the attack on one of the restaurants in the 10th arrondissement. Both were French nationals living in Belgium.

The prosecutor said the identities of the other assailants are under investigation.

Related: Paris Attackers Used Nearly Identical Explosive Devices: Prosecutor

The European Parliament in Brussels said Sunday it was stepping up security and raising its terror threat alert level, a day after officials in Belgium arrested five people in connection with the attacks.

“We consider this means they have a network,” Francoise Shepmans, mayor of the town of Molenbeek where the individuals were detained, told Belgium’s TV RTBF.

The broadening scope of the investigation came as more signs emerged that the attackers may have infiltrated Europe as part of the influx of refugees flooding the continent — bringing the immigration debate raging on the continent back to the fore.

Serbia's Ministry of Interior confirmed to NBC News that a terror suspect of interest to French authorities was registered and requested asylum at the Presevo border crossing on Oct. 7. The ministry would only give the suspect’s initials — A.A.

And A.A.’s details matched those of an individual registered in Greece four days earlier, the ministry added, saying that it was cooperating with French security services.

Greek police earlier said at least one of the attackers was linked to a passport that was registered on the island of Leros.

A black market for passports is booming in Syria, and officials have been concerned that ISIS militants and other radicals might be infiltrating Europe as part of a flood of refugees hitting the continent.

TIMELINE: How the Horror Unfolded in Paris

While it was unclear if the passport registered on Greece was legitimate, it raised the specter of further backlash in Europe against the tide of refugees. Officials are struggling to cope with the influx and opposition to welcoming refugees has grown amid signs some cities are overwhelmed.

As investigators worked furiously to chase down leads, France continued to mourn the heavy toll. Prime Minister Manuel Valls said that as of Sunday morning, authorities had identified 103 of the 129 people killed.

Valls met with relatives of victims at a counseling center set up at the historic Ecole MilItaire and told reporters there that all efforts were being made to offer support.

"Some families here are devastated, torn apart by pain," Valls told journalists after meeting with victims' loved ones. "Others know that their child has been killed but have no news at this stage because the body has not yet been identified."

A service was scheduled at Paris's famed Notre Dame Cathedral on Sunday and streams of people continued laying flowers and candles at impromptu memorials throughout Paris.

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Names of those who lost their lives also began to trickle out — along with tales of survival.

Julien Pearce, a French radio reporter who was at the Le Bataclan nightclub to watch the band Eagles of Death Metal, said concertgoers dropped to the floor and played dead as gunmen — three or four traipsed through the nightclub, he said — fired at random. After a few minutes on the ground, Pearce realized he would be killed if he didn't move. "We had to find an exit. At least to try," he said.