Spectators gather on the field of the Stade de France after the attacks. Photo: AP
Three teams carried out the attacks in the French capital which killed at least 129 people and left more than 350 wounded, a French official says.
Paris chief prosecutor Francois Molins on Saturday evening said, "We can say at this stage of the investigation that there were probably three co-ordinated teams of terrorists behind this barbaric act."
"We have to find out where they came from... and how they were financed," Molins told reporters.
He said that seven attackers had been killed, and that all had been heavily armed and wearing explosive belts.
Friday's attacks, claimed by Islamic State militants, hit a concert hall, a major stadium, restaurants and bars.
French Prime Minister Manuel Valls has said that France will continue with air strikes against the Islamic State in Syria and described the group as a very well-organized enemy.
Molins confirmed that one of the seven dead assailants was a French national named Ismael Omar Mostefai — a 29-year-old with a criminal record who had been previously monitored by French intelligence and linked to Islamist extremism. Mostefai was identified after his finger was found at the Bataclan concert hall and matched fingerprints the police had on file, AFP reported.
French police have taken Mostefai's father and brother into custody and searched their homes. Mostefai's older brother attended a police station voluntarily. "It's crazy, insane. I was in Paris myself last night, I saw what a mess it was," he told AFP before being placed in custody. He said that he had not had contact with his younger brother for several years.
Two others, a senior Belgian official said, appeared to be Belgian foreign fighters, including an 18-year-old who had fought in Syria.
A Syrian passport was found near the body of another assailant. Greek officials said that the passport holder had arrived in Europe in October along with a record flood of refugees fleeing the war-torn Middle East. The discovery immediately raised the prospect that militants may be using the same porous routes into Europe as migrants.
The extent of the violence signaled that the Islamic State is extending its reach far beyond the battlefields of the Middle East, prompting much of the rest of Europe to bolster security on Saturday, ramping up border checks and patrols at key buildings and transit points.
"The attacks mean the necessity of an even deeper revision of the European policy toward the migrant crisis," Konrad Szymanski, Poland's new European affairs minister, told a local radio station.
As if in response to the Saturday tough declaration in which French President Francois Hollande said that "France will be merciless in its response to the Islamic State militants", the Islamic State moments later asserted responsibility for the attacks.
In a statement issued on its internal social media site on Saturday, the Islamic State said that "eight brothers wearing explosive belts and carrying assault rifles" had carried out the attacks on "carefully chosen" targets, and were a response to France's involvement in the air strikes on Islamic State militants in Syria and Iraq.
"Let France and all nations following its path know that they will continue to be at the top of the target list of the Islamic State," it said.
Suspects arrested in Belgium
Belgian authorities made a number of arrests in the first publicized apprehensions after Friday night's bloodshed, a Belgian Justice Ministry spokeswoman said on Saturday.
In Belgium, raids were conducted in the Brussels suburb of Molenbeek-Saint-Jean, Justice Ministry spokeswoman Sieghild Lacoere said. A car rented in Brussels was found near one of the sites of the Paris attacks, and "that's what triggered the raids," Lacoere said.
In all, the raids took place in three homes in Molenbeek-Saint-Jean, a Western intelligence source told CNN.
At least one of the raids is connected to the Paris attacks, according to the source, who is in contact with French and Belgian intelligence services. The other raids are connected to individuals known to Belgium intelligence, the source said. Some of the Paris attackers are also known to Belgium intelligence, the source added.
A man who rented a VW Polo used by terrorists at the Bataclan concert venue was intercepted at the border with Belgium, Molins said. The man, who was driving a different vehicle when he was caught, is a French national living in Belgium and was accompanied by two other people, Molins said.
Response in wake of attacks
Hollande issued a state of emergency and called for three days of mourning after the attacks unfolded.
On Saturday, French Interior Minister Bernard Cazeneuve elaborated that the state of emergency could mean restrictions on people's movements. Border controls were tightened as of Friday, and the gendarmerie paramilitary police are on heightened alert, he said.
France has beefed up security forces at public transportation hubs, on the main roads and highways as well as everywhere in the center of Paris, Cazeneuve said after a meeting with Hollande.
On Saturday, candles and flowers filled an outdoor terrace at La Belle Equipe restaurant, where gunman shot into the crowd. Notes in the flowers included one that read, in French, "To our friend Guillaume full of joy and kindness, may God keep you close to him."
Another read: "Thoughts for our little Tess and to the children of Lacri. Their parents are in the stars."
Many Parisians — as they did after the attacks in January — vowed to hold firm. But some also questioned the wisdom of France's involvement in the Middle East.
"I'm indignant about the foreign policy of France,' Yannis Hassany, 25, a Parisian student of Syrian and Lebanese descent, said on Saturday. He was standing near the bloodstained streets of two of the attack sites, Le Carillon bar and Le Petit Cambodge restaurant. "What we've done the last four years is responsible for what happened here. France is implicated. France never should have gotten involved in Syria."