PARIS (AP / FOX 11) - French President Francois Hollande said Saturday that France would wage "merciless" war on the Islamic State group, after the jihadists claimed responsibility for a gun and bomb rampage targeting the vibrant cafes, bars and clubs of Paris -- an attack on the heart of the City of Light that killed more than 120.
Grief, alarm and resolve spread across Europe as officials raced to piece together information on the attackers. Officials said one was a young Frenchman known to the authorities; a Syrian passport found near the body of another was linked to a man who entered the European Union through a Greek island last month.
Hollande said at least 127 people died Friday night when attackers launched gun attacks at Paris cafes, detonated suicide bombs near France's national stadium and killed hostages inside a concert hall during a rock show. More than 200 people were hurt, dozens critically.
"These places are the places we visit every week," said Ahsan Naeem, a 39-year-old filmmaker who has lived in Paris for seven years. "Streets we walk every day.
"All those places will have been full of my people. My friends. My acquaintances."
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."
Hollande said France would increase its military efforts to crush IS. He said France -- which is part of a U.S.-led coalition bombing suspected IS targets in Syria and Iraq and also has troops fighting militants in Africa -- "will be merciless toward the barbarians of Islamic State group."
The Islamic State group claimed responsibility in an online statement in Arabic and French circulated by 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."
Many of Paris's top tourist attractions closed Saturday, including the Eiffel Tower, the Louvre Museum and the Disneyland theme park east of the capital. Some 3,000 troops were deployed to help restore order and reassure a frightened populace.
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.
The attacks, on an unusually balmy November Friday evening, struck at the heart of Parisian life: diners in cafes, concertgoers watching a rock band, spectators at a soccer match.
Paris Mayor Anne Hidalgo said the places attacked are ones Parisians love, where they celebrate diversity.
"It is this Paris that was hit, probably because this example of living together, which is so strong in our city, is unbearable for fanatical people," she said.
Parisians expressed shock, disgust and defiance in equal measure. Some areas were quiet, but hundreds queued outside a hospital near the Bataclan concert hall, scene of the worst violence, to donate blood. As a shrine of flowers expanded along the sidewalk, a lone guitarist sang John Lennon's peace ballad, "Imagine."
Authorities said eight attackers 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.
Authorities in Belgium conducted raids in a Brussels neighborhood Saturday and made several arrests linked to the Paris attacks. Justice Minister Koen Geens told the VRT network that the arrests came after a car with Belgian license plates was seen close to the Bataclan theater.
French officials said a suicide bomber at the concert hall was identified as a young Frenchman flagged in the past for links with an Islamic extremist activity, and a Syrian passport was recovered from the remains of another suicide bomber outside the stadium.
Officials in Greece said the attacker with the Syrian passport had entered in October through Leros, one of the islands that tens of thousands of people fleeing war and poverty in Syria and elsewhere have been using as a gateway to the European Union in recent months.
If the attack does involve militants who traveled to Europe amid millions of refugees from the Middle East, the implications could be profound.
Poland's prospective minister for European affairs, Konrad Szymanski, said that in light of the attacks, Poland would not comply with an EU plan to accept refugees unless it received "guarantees of security."
The attack brought an immediate tightening of borders as Hollande declared a state of emergency and announced renewed border checks along frontiers that are normally open under Europe's free-travel zone.
The militants launched at least six gun and bomb attacks in rapid succession on apparently indiscriminate civilian targets.
Three suicide bombs targeted spots around the national Stade de France stadium, in the north of the capital, where Hollande was watching a France-Germany soccer match. Fans inside the stadium recoiled at the sound of explosions, but the match continued.
Around the same time, fusillades of bullets shattered the clinking of wine glasses in a trendy Paris neighborhood as gunmen targeted a string of crowded cafes.
The attackers next stormed the Bataclan concert hall, which was hosting the American rock band Eagles of Death Metal, originally from Palm Desert, California. They opened fire on the panicked audience and took members hostage. As police closed in, three detonated explosive belts, killing themselves, according to Paris police chief Michel Cadot.
Another attacker detonated a suicide bomb on Boulevard Voltaire, near the music hall, the prosecutor's office said.
The wife of the band's drummer Julian Dorio told the Washington Post that Dorio and other band members of Eagles of Death Metal were safe.
The band's Facebook page later posted an update:
"We are still currently trying to determine the safety and whereabouts of all our band and crew. Our thoughts are with all of the people involved in this tragic situation."
Video shot posted by newspaper Le Monde Saturday captured some of that horror as dozens of people fled from gunfire outside the Bataclan down a passageway to a side street.
At least one person lies writhing on the ground as scores more stream past, some bloodied or limping. The camera pans down the street to reveal more fleeing people dragging two bodies along the ground. A woman and two others can be seen clinging to upper-floor balcony railings in an apparent desperate bid to stay out of the line of fire.
Le Monde said its reporter Daniel Psenney filed the scene from his apartment balcony, and was shot in the arm when he went downstairs to help someone who had collapsed.
A tall, sturdy 38-year-old concert-goer named Sylvain collapsed in tears as he recounted the attack, the chaos and his escape during a lull in gunfire.
"First I heard explosions, and I thought it was firecrackers," he said.
"Very soon I smelled powder, and I understood what was happening. There were shots everywhere, in waves. I lay down on the floor. I saw at least two shooters, but I heard others talk. They cried, 'It's Hollande's fault.' I heard one of the shooters shout, 'Allahu Akbar,'" Sylvain told The Associated Press. He spoke on condition that his full name not be used out of concern for his safety.
The Paris carnage was the worst in a series of attacks claimed by the Islamic State in the past three days. On Thursday, twin suicide bombings in Beirut killed at least 43 people and wounded more than 200, and 26 people died Friday in Baghdad in a suicide blast and a roadside bombing that targeted Shiites.
The militant group also said it bombed a Russian plane that crashed in Egypt's Sinai Peninsula on Oct. 31, killing 224 people.
IS also suffered significant reversals this week, with Kurdish forces launching an offensive to retake the strategic Iraqi city of Sinjar and the U.S. military saying it had likely killed Mohammed Emwazi, the masked British-accented militant known as "Jihadi John" who is seen in grisly IS beheading videos.
France has been on edge since January, when Islamic extremists attacked the satirical newspaper Charlie Hebdo, which had run cartoons of the Prophet Muhammad, and a kosher grocery. Twenty people died in those attacks, including three shooters.
French authorities are particularly concerned about the threat from hundreds of French Islamic radicals who have traveled to Syria and returned home with skills to mount attacks.
"The big question on everyone's mind is: Were these attackers -- if they turn out to be connected to one of the groups in Syria -- were they homegrown terrorists or were they returning fighters?" said Brian Michael Jenkins, a terrorism expert and senior adviser to the president of the Washington-based RAND Corporation.