PARIS (AP) — French President Francois Hollande vowed to attack the Islamic State group without mercy as the jihadist group admitted responsibility Saturday for orchestrating the deadliest attacks on France since World War II.

He said at least 127 people died Friday night in shootings at Paris cafes, suicide bombings near France's national stadium and a hostage-taking inside a concert hall. Another 200 or so were injured, dozens critically.

Hollande, who declared three days of national mourning and raised the nation's security to its highest level, called the carnage "an act of war that was prepared, organized, planned from abroad with internal help."

The Islamic State group's claim of responsibility appeared in Arabic and French in an online statement circulated by IS supporters. It was not immediately possible to confirm the authenticity of the admission, which bore the group's logo and resembled previous verified statements from the group. The statement mocked France's involvement in air attacks on suspected IS bases in Syria and Iraq, noting that France's air power was "of no use to them in the streets and rotten alleys of Paris."

As Hollande addressed the nation, French anti-terror police worked to identify potential accomplices to the attackers, who remained a mystery to the public: their nationalities, their motives, even their exact number. Police said a Syrian passport was recovered from the remains of one suicide bomber outside the stadium.

Authorities said eight died, seven in suicide bombings, a new terror tactic in France. Police said they shot and killed the other assailant.

Prosecutor's office spokeswoman Agnes Thibault-Lecuivre said authorities couldn't rule out the possibility that other militants involved in the attack remained at large.

The violence raised questions about security for the millions of tourists who come to Paris and for world events routinely hosted in the normally luminous capital, where 1,500 troops were deployed to support police in restoring order and reassuring a frightened populace.

French Interior Minister Bernard Cazeneuve announced that all public demonstrations would be banned until Thursday and local governments would have the option to impose nightly curfews. He said police and military reinforcements would be deployed to key public buildings.

Many of Paris' top tourist attractions closed Saturday, including the Eiffel Tower, the Louvre Museum and the Disneyland theme park east of the capital.

Parisians expressed shock, disgust and defiance in equal measure. Hundreds of soccer fans departing the stadium Friday night waved French flags and sang impromptu choruses of the national anthem, "Le Marseillaise." The next morning, hundreds queued outside a hospital near the Bataclan theater, scene of the most appalling violence, to donate blood. As a shrine of flowers expanded along the sidewalk, a lone guitarist sang John Lennon's peace ballad, "Imagine."

Hollande said the attacks meant France would increase its military efforts to crush IS. He said France — which besides bombing suspected IS targets in Syria and Iraq as part of the U.S.-led coalition also has troops fighting militants in Africa — "will be merciless toward the barbarians of Islamic State group."

Reflecting fears in other European capitals of the risk of coordinated or copycat attacks, the British government mounted a meeting of its own emergency COBRA intelligence committee. Italy said it, too, was raising security levels on borders and major public places.

British Prime Minister David Cameron said British citizens were among the casualties in Paris, but he declined to provide specifics. He warned that the threat posed by Islamic State "is evolving."

Friday night's militants launched at least six gun and bomb attacks in rapid succession on apparently indiscriminate civilian targets.