PARIS • Police investigating a wave of terror attacks in Paris on Friday have launched an international hunt for a man they believe might have helped organise the deadly assaults, in which one of his brothers has been identified as a gunman.

The authorities were seeking Salah Abdeslam, 26, describing him as dangerous with the police warning the public: "Do not intervene on your own, under any circumstances."

Belgian officials said that his brother Ibrahim had died in the three-hour massacre. Another brother, Mohamed, was detained in the Molenbeek area of Brussels on Saturday but then released yesterday "without being charged", a spokesman for the prosecutor told the Agence France-Presse (AFP) news agency.

The carefully coordinated attacks on Friday night, which killed at least 129 people and are believed to be the work of the Islamic State in Iraq and Syria (ISIS), increasingly appear to have involved extensive planning by a network of men with sophisticated weapons who plotted the attack from outside the country.

Meanwhile, other French investigators are studying the possibility that Abdelhamid Abaaoud, a Belgian citizen, may also have been an organiser of the attacks, the Paris prosecutor's office said. He is believed to be fighting in Syria. But Mr Eric van der Sypt, a Belgian federal magistrate, told the New York Times that reports that the authorities had homed in on Abaaoud, were premature.

The French interior minister, Mr Bernard Cazeneuve, after meeting in Paris with his Belgian counterpart, Mr Jan Jambon, said the attackers had "prepared abroad and had mobilised a team of participants located on Belgian territory, and who may have benefited - the investigation will tell us more - from complicity in France".

French officials initially said eight attackers died on Friday, but on Saturday night said that only seven were dead - six by detonating suicide bombs and one in a shoot-out with the police.

On Sunday, intelligence officials said they were looking for an eighth man believed to have been involved in the attacks, and hours later, the police released Salah Abdeslam's name and photo.

The Abdeslam brothers lived in Molenbeek, an impoverished section of Brussels that is mostly populated by immigrants from the Arab world and that has been linked to violence. Other suspects of recent terror attacks also had links to Molenbeek.

The militants included Amedy Coulibaly who was believed to have bought weapons in Molenbeek, and was later involved in the assault on a Jewish supermarket in January. Another is Mehdi Nemmouche, a Frenchman who bought weapons there and attacked the Jewish Museum of Belgium last year.

Ayoub El Khazzani, a Moroccan who was stopped while trying to attack passengers on a high-speed train travelling to Paris from Amsterdam, Netherlands, is also thought to have lived in Molenbeek.

Meanwhile, crucial if sparse details about the other attackers have also emerged.

Police named just two French attackers - Ismael Omar Mostefai, 29, from Chartres, south-west of Paris, and Samy Amimour, 28, from the Paris suburb of Drancy.

Mostefai was the middle of five children born to an Algerian father and a Portuguese mother, and he once worked at a bakery, according to a former neighbour at the housing development just outside Chartres where the family used to live.

"They were a normal family, just like everybody else," said the neighbour, who spoke on the condition of anonymity.

"It was in 2010, that's when he started to become radicalised," the neighbour said.

A Turkish official said the police there had twice warned France about Mostefai.

Amimour was charged in 2012 with "conspiracy to commit terrorism" over a planned attack in Yemen that was foiled. He violated his judicial supervision in 2013, prompting judges to issue an international arrest warrant.

His family told AFP, in an interview before Friday's attacks in Paris took place, that he had gone to Syria in 2013.

The media named another French assailant as Bilal Hadfi, who blew himself up outside the national stadium. The 20-year-old was reported to have fought alongside ISIS. Another attacker - whose nationality is not yet known - evidently posed as a Syrian migrant. The Serbian newspaper Blic published a photograph of a passport page that identified its holder as Ahmad al-Mohammad, 25, a native of Idlib, Syria.

He passed through the Greek island of Leros on Oct 3 and the Serbian border town of Presevo on Oct 7, officials in those countries said. It was not clear whether the passport was authentic.

Salah Abdeslam and two other men passed through a roadside check in Cambrai, France, at 9.10am Saturday, while on a highway heading to Belgium.

They made their way to Molenbeek, where the authorities seized the car later on Saturday afternoon and arrested his companions and, separately, his brother.

It was not clear how Abdeslam got away.

NEW YORK TIMES, REUTERS, AGENCE FRANCE-PRESSE