Three Kalashnikov rifles have been found in an abandoned car believed to have been used in the Paris gun and bomb attacks, according to reports.
Officials said a Seat car had been found in the Paris suburb of Montreuil, but they could not confirm if this was the black Seat linked to the attacks on the Le Carillon Bar and Le Petit Cambodge restaurant.
It comes as a French citizen - Ismael Omar Mostefai - was named as one of the terrorists who was reportedly inside the Bataclan concert hall where at least 89 people died.
At least seven people have now been detained in Belgium and on the Belgian-French border, but Belgian officials have declined to comment on reports the attacks were largely planned in Brussels.
A French official said a brother of one of the suicide bombers was among those facing questioning.
Investigators are trying to identify all seven attackers, and any potential accomplices.
According to French news website RTL, Mostefai's brother turned up at a police station near his home in the south of Paris explaining that he had not been heard from in months. Former neighbours described Mostefai as "a bloke like any other".
Paris prosecutor's office said some of Mostefai's family members had been held, without giving details.
French newspaper Le Monde reported he was identified by his fingertip, discovered after he detonated a suicide vest inside the Bataclan concert venue as police closed in.
Mostefai was born in Courcouronnes, Essonne, on 21 November 1985, and lived in Chartres, southwest of Paris.
Paris prosecutor Francois Molins said he had a criminal record and was known to security services but had not spent time in jail.
Mr Molins said: "He caught police's attention due to the violation of public power. From 2004 to 2010, he was pronounced guilty eight times, but has never been in prison.
"In 2010, he was blacklisted by the police due to extreme behaviours, but never been classified into any illegal extremist groups."
Three teams of attackers in identical explosives vests seem to have co-ordinated the "act of barbarism" that left a total 129 people dead and 352 injured across the French capital, Mr Molins said.
One Irish person was among those injured in the attacks. Foreign Affairs Minister Charlie Flanagan says the individual is believed to be in a stable condition.
Three days of mourning are underway in France for the victims of the Paris attacks. Here in Ireland, flags will fly at half mast in solidarity with those affected.
Parisians have been gathering near the Bataclan theatre, where around 80 people were killed to pay their respects:
People light candles while outside The Belle Equipe restaurant in Paris. Image: Daniel Ochoa de Olza / AP/Press Association Images
A French citizen is among three people detained at the Belgian border, while others were held in police raids in Molenbeek, an immigrant area of Brussels.
Belgian Prime Minister Charles Michel said at least one of those held in Molenbeek was thought to have spent the previous night in Paris.
Two cars registered in Belgium were impounded close to scenes of some of the violence in Paris, including the Bataclan.
Molenbeek has been connected with two attacks in France this year - the Islamist killer at a kosher shop in Paris in January got his guns in the district, as did the attacker overpowered on a Brussels-Paris train in August.
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".
French President Francois Hollande earlier said the assaults were an "act of war" by IS.
Syrian and Egyptian passports were found near the bodies of two of the attackers, with Greek officials suggesting that two of the suspects may have arrived in the European Union through Greece in recent months. However, experts say it is possible the passports were faked or stolen from innocent people.
French Prime Minister Manuel Valls has vowed to "destroy" those behind the killings.
"We will strike this enemy to destroy him. In France and in Europe, we'll chase the authors of this act, and also in Syria and Iraq. We will win this war," he said.
Thousands of soldiers have been deployed on the country's streets in the aftermath of the attacks.
Speaking on the Colette Fitzpatrick Show earlier this morning, French Ambassador to Ireland - Jean-Pierre Thébault - said that France will respond in due course to the Paris attacks:
