PARIS — French President Francois Hollande on Saturday blamed the Islamic State terror group for the attacks in Paris that left at least 128 people dead, calling them an "act of war" organised from abroad with internal help.
"Faced with war, the country must take appropriate action," he said, without elaborating. Mr Hollande said he would address parliament on Monday and the country would observe three days of official mourning for the victims of Friday's mayhem.
The multiple attacks across the capital were "an act of war ... committed by a terrorist army, the Islamic State, against France, against ... what we are, a free country," Hollande said.
The president also declared a state of emergency, saying he was closing the country's borders. However, officials later said they were just reimposing border checks that had been removed after Europe created its Schengen free-travel zone in the 1980s.
Islamic State claimed responsibility for the attacks in a statement posted online on Saturday.
It said "eight brothers wearing explosive belts and carrying assault rifles" conducted a "blessed attack on ... Crusader France", with the targets "carefully chosen".
The statement, published in both Arabic and French, threatened further attacks against France "as long as it continues its Crusader campaign".
It said France was guilty of "striking Muslims in the caliphate with their aircraft".
France was reeling after a night of horror when gunmen sprayed restaurants with bullets, massacred scores of concert-goers and launched suicide attacks near the national stadium.
At least eight militants, all wearing suicide vests, brought unprecedented violence to the streets of the French capital, in the bloodiest attacks in Europe since the Madrid train bombings in 2004.
Armed with AK47s and shouting "Allahu akbar", four of the group marched into a rock concert at the Bataclan concert hall in eastern Paris, murdering at least 82 people and taking dozens hostage.
"They didn't stop firing. There was blood everywhere, corpses everywhere. Everyone was trying to flee," said Pierre Janaszak, a radio presenter who was at the concert by US rock band Eagles of Death Metal.
Hinting at their motives, the gunmen were overheard raging at President Hollande and his military interventions in the Syrian civil war against Islamic State.
"I clearly heard them say 'It's the fault of Hollande, it's the fault of your president, he should not have intervened in Syria'," Janaszak added.
More than 500 French fighters are thought to be with Islamic State in Syria and Iraq, according to official figures, while 250 have returned and some 750 expressed a desire to go.
Islamic State, meanwhile released an undated video on Saturday urging Muslims to attack France.
In January, 17 people were killed in Paris in attacks that targeted the satirical magazine Charlie Hebdo and a Jewish supermarket. Another disaster was narrowly averted in August when a gunman was overpowered on a packed high-speed train in northern France.
No arrests had been made by early Saturday morning and it was unclear if any gunmen were still on the loose. Police were screening hours of video surveillance footage at the multiple locations. As a precaution, all sports events were cancelled on Saturday in Paris, while access to public facilities such as museums and swimming pools was restricted.
"Terrorist attacks of an unprecedented level are under way across the Paris region," Hollande said in an emotional televised message on Friday night in which he declared a nation-wide state of emergency. "It's a horror," he added.
The president himself was caught up in the carnage and had to be hastily evacuated from the national Stade de France stadium when suicide bombers struck outside during a friendly football international between France and Germany.
At first, very few of the crowd appeared to be aware of the significance of what was happening despite the appearance of helicopters low in the sky. The match continued as other attacks began around the capital.
The worst of the bloodshed occurred at the Bataclan music venue in the trendy 11th arrondissement where more than 1,000 rock fans were at a sold-out show for the Eagles of Death Metal band.
Four gunmen wearing suicide vests and armed with automatic weapons stormed the venue and began spraying the crowd with bullets. As screams rang out and survivors ran over the injured or dead to make their ways to the exits or places to hide, the militants took hostages and then began executing them.
"We heard people screaming — the hostages particularly — and the threats from the kidnappers," added another survivor, 34-year-old Charles.
Along with around 20 others, he fled to a washroom where he pushed through the ceiling and hid in the crawl space.
Three of the militants blew up their explosive vests as anti-terror police raided the venue around 12.30am, while a fourth was shot dead.
Another attacker blew himself up in nearby Boulevard Voltaire, as the streets were filled with the sound of police sirens and convoys of ambulances shipping hundreds of injured to hospital.
Several restaurants near the concert hall were also targeted, including a popular Cambodian eatery in the trendy Canal St. Martin area, whose bars and restaurants heave with the young and affluent on a typical Friday night.
An extra 1,500 soldiers were mobilised to reinforce police in Paris, Hollande's office said, with the city still recovering from the psychological wounds inflicted by the Charlie Hebdo attack.
French media reacted with horror but determination to the scenes of devastation. "War in central Paris," the daily newspaper Le Figaro declared, with Le Parisien taking up a similar theme: "This time it's war."
"In the name of the true martyrs of yesterday, the innocent victims and in the name of the Republic, France will be able to stay united and stand together," said Le Parisien.
The "terrorist barbarism" has crossed a "historic line", said the left-leaning newspaper Liberation, calling for France to stay resolute. There was no immediate claim of responsibility for the attacks.
Other reactions were a mix of fear and defiance.
Concert-goer Charles, who spoke to AFP at the Bataclan, said he would refuse to be cowed by the terror he had experienced. "Life goes on. We won't give in to fear. F#*@ them!" he said. "I'm going to a concert on Tuesday. Keep rocking!"
US President Barack Obama led a chorus of global condemnation, saying it was "an attack on all of humanity", and New York lit the World Trade Center in the red, white and blue of the French flag.
German Chancellor Angela Merkel and European Commission chief Jean-Claude Juncker said they were "deeply shocked" by the attacks.
Security had begun to be stepped up ahead of key UN climate talks to be held just outside the French capital from Nov 30, with border checks restored from Friday. France has joined US-led air strikes on IS targets in Iraq for over a year and in September began bombing the jihadists in Syria.
Police secure the area around the Bataclan concert hall after the shootings. (Reuters photo)