LONDON -- French President Francois Hollande told his shell-shocked nation Saturday morning that the carnage Friday night in Paris was an "act of war" committed by the Islamic State of Iraq and Syria (ISIS).

"It's an act of war that was prepared, organized, planned from the outside and with accomplices on the inside," Hollande said in a live television address. He declared three days of mourning and put France's security agencies at their highest level of alert.

Less than an hour later, ISIS released its official statement claiming responsibility for the onslaught, calling it a "blessed invasion."

The well-coordinated series of terror attacks on Paris left more than 129 people dead, almost 100 more with serious injuries and double that number with minor wounds, according to French officials.

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Two French police officials said that authorities have identified one of the suicide bombers who targeted Paris as a young Frenchman flagged in the past for links with an Islamic extremist activity.

The officials said the man was among attackers who blew himself up after a rampage and hostage-taking in a Paris concert hall.

Earlier, a U.S. intelligence official confirmed to CBS News that part of a Syrian passport was recovered where suicide bombers struck near France's national soccer stadium. The official said a name and picture were recovered and the individual was not known to intelligence officials.

However, a U.S. intelligence official later told CBS News that the passport might be fake. The passport didn't contain the correct numbers for a legitimate Syrian passport, and the picture didn't match the name.

None of the attackers has been publicly identified.

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.

ISIS is known to have been working on capabilities to attack Western Europe.

The group claims to have been behind the apparent bombing of a Russian jetliner that crashed in Egypt's Sinai Peninsula at the end of October, and U.S. officials say it's very likely that claim is legitimate.

ISIS' statement said a total of eight men "wearing suicide belts and machine guns" carried out the mission. Late Saturday, a French prosecutor said seven attackers were killed.

Suspicion quickly turned to Islamic extremists as the mayhem unfolded. They're angry at France's military operations against ISIS and al Qaeda affiliates in Syria.

ISIS and AQAP, al Qaeda's franchise in Yemen, were behind the attacks on satirical newspaper Charlie Hebdo this year and have hit Jewish and other sites in France in the past.

ISIS' Al-Hayat Media Center released a video Saturday featuring a bearded French-speaking militant, warning French citizens that, "as long as you keep bombing you will not live in peace. You will even fear traveling to the market." It was not clear, however, when the video was recorded.

Senior CBS News contributor and former deputy CIA director Mike Morell told Scott Pelley on the "CBS Evening News" Friday night that the attack was clearly well-coordinated.

"We're talking about a large group of them. We're talking about multiple simultaneous attacks, and they kept it secret; that is a very difficult thing to do," Morell said. "It requires operational sophistication. We haven't seen that level of sophistication since the London bombings [of 2005].

Morell noted that ISIS "has been working on a capability to conduct attacks in Western Europe." AQAP already proved that capability with the attack on Charlie Hebdo.

If ISIS role in the attacks is certain, it could be indicative of a new and more structured effort by the group to project its influence well beyond the borders of the territory it holds in Iraq and Syria, says CBS News' Khaled Wassef, who monitors jihadist groups' activities closely.

In recent weeks, ISIS is believed to have inflicted more casualties in attacks carried out abroad -- taking into account the Russian plane, deadly bombings in Ankara, Turkey, and the Lebanese capital of Beirut -- than those carried out in Syria and Iraq combined.

The group has faced an increasing challenge on its own territory as Russia backs Syrian President Bashar Assad's forces in that country, and the U.S. military throws its weight behind Kurdish troops battling to reclaim ground from the terror group in northern Iraq.

There has been concern among European officials -- muted, perhaps by the overwhelming scale of the humanitarian catastrophe -- that ISIS and other terror groups operating in North Africa and the Middle East could try and sneak trained militants back into Europe amid the flood of migrants and refugees reaching the continent this year.

About 800,000 people have poured into southern Europe already in 2015, most of them by crossing the Mediterranean in over-packed boats set on a course for Italy or Greece by smugglers who charge hundreds or even thousands of dollars for a place on the risky journeys.

French authorities have closed the Eiffel Tower and other top tourist sites in Paris until further notice.

A Louvre spokeswoman said the museum opened as normal on Saturday, with enhanced security, but was ordered closed by the Culture Ministry after President Francois Hollande called for national day of mourning.

Leading French movie theater chains are shutting their Paris cinemas after attacks on a concert hall, stadium and cafes that left at least 127 people dead.

The UGC and Gaumont Pathe chains said in tweets that they would close their Paris movie theaters for a day Saturday after the bloodshed Friday night in the French capital.

Several entertainment and cultural sites in Paris have also closed their doors Saturday, including Disneyland Paris, the Eiffel Tower and the Louvre Museum.

The rock band U2 postponed its Saturday night concert in Paris in light of the deadly attacks. HBO had planned to televise the band's performance. Instead, U2 said in a statement that it is resolved to go ahead with the concert "at an appropriate time."

The Foo Fighters also canceled the rest of their European tour following the deadly attacks in Paris.

The band said in a statement Saturday that "it is with profound sadness and heartfelt concern for everyone in Paris that we have been forced to announce the cancellation of the rest of our tour."

The group, led by Dave Grohl, were to play at the Accor Hotels Arena in Paris on Monday and in Casalecchio Di Reno, Italy, on Friday; other canceled shows include stops in Turin, Italy; Lyon, France; and Barcelona, Spain.

"In light of this senseless violence, the closing of borders, and international mourning, we can't continue right now. There is no other way to say it," the statement read. "This is crazy and it sucks. Our thoughts and prayers are with everyone who was hurt or who lost a loved one."

Former U.S. Vice President Al Gore, who was in Paris when the attacks took place, says he is suspending the broadcast of a climate change event scheduled for this weekend.

However, French Foreign Minister Laurent Fabius said a crucial U.N. conference on fighting climate change will be held in Paris as planned, "with enhanced security measures," from Nov. 30 to Dec. 11.

So far 127 world leaders have accepted the invitation to come to Paris for the climate conference.