ISIS Claims 'Blessed Invasion' Of Paris

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 it's official statement claiming responsibility for the onslaught, calling it a "blessed invasion."

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.

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

An American college student from California is one of the dead.

11/14/201 Related Story: American Killed In Paris Terror Attacks

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.

Police in the French capital were still hunting Saturday morning for any possible attackers or accomplices linked to the six separate attacks. Eight terrorists were killed -- seven of them by suicide bombs and one by police.

ISIS' statement said a total of eight men "wearing suicide belts and machine guns" carried out the mission.

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.

The Associated Press, citing two unnamed French police officials, reported Saturday that authorities found a Syrian passport on the body of a suicide bomber who targeted France's national soccer stadium.

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.

11/14/2015 Related Story: Belgium: Authorities Make Arrests Tied To Paris Attacks

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.