French President Francois Hollande said on Saturday the attacks in Paris that killed 127 people were "an act of war" organised from abroad by Islamic State with internal help.

"Faced with war, the country must take appropriate action," he said, without saying what that meant.

The attacks at a stadium, concert hall and cafes and restaurants in northern and eastern Paris were "an act of war committed by Daesh that was prepared, organized and planned from outside (of France)" with help from inside France, Hollande said, using the Arabic acronym for Islamic State.

Hollande's statement came after the Islamic State militant group claimed responsibility on Saturday for attacks that killed 127 people in Paris.

In an official statement, the terror group said its fighters strapped with suicide bombing belts and carrying machine guns carried out the attacks in various locations in the heart of the capital which were carefully studied.

Hollande said he would address parliament on Monday in an extraordinary meeting and the country would observe three days of official mourning for the victims of Friday's attacks.

"All measures to protect our compatriots and our territory are being taken within the framework of the state of emergency," he said.

Islamic State also released an undated video on Saturday urging Muslims to attack France.

The co-ordinated assault on Friday evening came as France, a founder member of the US-led coalition waging air strikes against Islamic State fighters in Syria and Iraq, was on high alert for terrorist attacks ahead of a global climate conference due to open later this month.

It was the worst such attack in Europe since the Madrid train bombings of 2004, in which 191 died.

Hollande said the death toll stood at 127. Officials said eight assailants had died, seven of whom had blown themselves up with explosive belts at various locations, while one had been shot dead by police. It was not clear if all the attackers were accounted for.

"The terrorists, the murderers raked several cafe terraces with machine-gun fire before entering (the concert hall). There were many victims in terrible, atrocious conditions in several places," police prefect Michel Cadot told reporters.

After being whisked from the stadium near the blasts, Hollande declared a national state of emergency - the first since World War Two. Border controls were temporarily reimposed to stop perpetrators escaping.

Local sports events were suspended, the rock band U2 canceled a concert, the Paris metro railway was closed and schools, universities and municipal buildings were ordered to stay shut on Saturday. However some rail and air services were expected to run.

"This is a horror," the visibly shaken president said in a midnight television address to the nation before chairing an emergency cabinet meeting.

He later went to the scene of the bloodiest attack, the Bataclan music hall, and vowed that the government would wage a "merciless" fight against terrorism.

Sylvestre, a young man who was at the Stade de France when bombs went off there, said he was saved by his cellphone, which he was holding to his ear when debris hit it.

“This is the cell phone that took the hit, it's what saved me," he said. "Otherwise my head would have been blown to bits," he said, showing the phone with its screen smashed.

French newspapers spoke of "carnage" and "horror". Le Figaro's headline said: "War in the heart of Paris" on a black background with a picture of people on stretchers.

Emergency services were mobilized, police leave was canceled, 1,500 army reinforcements were drafted into the Paris region and hospitals recalled staff to cope with the casualties.

Radio stations warned Parisians to stay at home and urged residents to give shelter to anyone caught out in the street. The hashtag #porteouverte (open door) started up on Twitter to offer people a place to stay.

The deadliest attack was on the Bataclan, a popular concert venue where the Californian rock group Eagles of Death Metal was performing. The hall is near the former offices of the satirical weekly Charlie Hebdo, target of a deadly attack by Islamist gunmen in January.-Reuters