Last Updated Nov 14, 2015 10:30 PM EST
PARIS -- Three teams of extremists carried out the coordinated gun-and-suicide bombing attacks across Paris that left 129 people dead and 352 injured, a French prosecutor said Saturday.
Paris prosecutor Francois Molins said 99 of the injured were in critical condition after the "act of barbarism." He said the attackers in the Bataclan concert hall, where 89 people died, mentioned Syria and Iraq during their deadly rampage.
French President Francois Hollande has vowed that France will wage "merciless" war on the Islamic State of Iraq and Syria, or ISIS, after the jihadists claimed responsibility for the attacks Friday night.
Grief, alarm and resolve spread across Europe on Saturday as officials raced to piece together information on the seven attackers. Officials said one was a young Frenchman known to the authorities. In addition, a Syrian passport found near the body of another attacker was linked to a man who entered the European Union through a Greek island last month.
However, a U.S. intelligence official told CBS News the Syrian passport might be fake. The official said the passport did not contain the correct numbers for a legitimate Syrian passport and the picture did not match the name.
A U.S. law enforcement source told CBS News senior investigative producer Pat Milton French law enforcement officials were taking DNA and fingerprints from the dead terrorists. The test results were being run through databases as part of effort to identify the terrorists and their networks.
A U.S. Intelligence source told Milton investigators have so far seen no insider knowledge in the chatter or communications that is being intercepted to verify who was involved. While there have been people saying glowing things about the Paris attack, no one has revealed information about the attack that only the attackers would have knowledge of, the source said.
The FBI is sending a four or five additional FBI agents to Paris to bolster its small office there, an official confirms to CBS News. They have expertise in computer and evidence forensics.
However, the FBI is not joining the investigation. The French have not asked for their assistance.
The FBI has taken similar steps in the past following major overseas events.
Friday night, attackers launched a series of coordinated, nearly simultaneous attacks: opening fire at Paris cafes, detonated suicide bombs near France's national stadium and killing hostages inside a concert hall during a rock show - an attack on the heart of the pulsing City of Light.
"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."
It appears the Stade de France, north of the city, was to be the main target but the attack didn't go as planned. Security officials believe the terrorists intended to assault the crowd of 80,000 as they poured in to see a big match between France and Germany.
For unknown reasons, the bombers were late to the game, so they detonated their bombs in a much smaller crowd. One of them was a propane tank in a backpack loaded with screws and bolts. One security source tells CBS News the bombs at all six locations killed very few victims - nearly all the dead were shot with Kalashnikov machine guns.
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. 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.
A U.S. law enforcement official said the attack was well organized but not sophisticated. Investigators are not seeing ingenious explosive devices, rather rudimentary ones, reports Pat Milton.
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 president said France would increase its military efforts to crush ISIS. He said France - which is part of a U.S.-led coalition bombing suspected ISIS targets in Syria and Iraq and also has troops fighting militants in Africa - "will be merciless toward the barbarians of Islamic State group."
ISIS claimed responsibility in an online statement in Arabic and French circulated by supporters.
The statement mocked France's involvement in air attacks on suspected ISIS 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' top tourist attractions closed down 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 - and ones 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 to donate blood. As a shrine of flowers expanded along the sidewalk, a lone guitarist sang John Lennon's peace ballad "Imagine."
Authorities said seven attackers died in suicide bombings, a new terror tactic in France. Police said they shot and killed the other assailant.
Molins, the prosecutor, said all the suicide attackers wore identical explosives vests.
Authorities in Belgium conducted raids in a Brussels neighborhood Saturday and made three 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.
In addition, the governor of Bavaria said the arrest of a man in Germany last week may be linked to the Paris attacks. A spokesman for Bavarian state police spokesman confirmed that firearms, explosives and hand grenades were found when undercover police stopped a man near the German-Austrian border on Nov. 5.
Ludwig Waldinger declined to confirm reports by public broadcaster Bayrischer Rundfunk that the man appeared to be en route to Paris when he was arrested. Bavarian governor Horst Seehofer told reporters Saturday there were "reasonable grounds" to assume that there may be a link to the Paris attacks.
CBS News' Investigative Unit can confirm that American law enforcement is looking into the man arrested in Bavaria. They have been in contact with Bavarian police on this, as well as Montenegrin police, as he is a citizen of Montenegro. It appears he would not talk with police and is possibly still in detention in Germany.
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. Germany also stepped up border checks.
Video shot posted by newspaper Le Monde Saturday captured some of that horror as dozens of people fled from gunfire outside the Bataclan.
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 a desperate bid to stay out of the line of fire.
Le Monde said its reporter Daniel Psenney filmed 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.
A U.S. source told CBS News two Americans are known to have been injured in the attacks.
A male American suffered a leg injury that wasn't believed to be life-threatening, the source said. He was receiving medical care and has been in touch with his family in the U.S.
An American woman, Helen Jane Wilson, was undergoing surgery late Saturday after being shot in the leg.
Wilson told The Associated Press she was at the Bataclan concert hall to hear the Eagles of Death Metal band perform Friday night when gunmen burst into the venue, killing 89 people. was shot in the leg and was heading into surgery at L'hopital Saint-Antoine.
Wilson said she lived in New Orleans before moving to Paris, where she runs Rock en Bol, a catering company. According to her Facebook page, Wilson is originally from Los Angeles.
The Paris carnage was the worst in a series of attacks claimed by ISIS 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.
ISIS 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 ISIS 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.