Paris (CNN)ISIS has claimed responsibility for the worst violence witnessed in France since World War II, a volley of nearly simultaneous terror attacks that the French President called "an act of war."

The assailants targeted six sites Friday night in Paris, the deadliest being a massacre at a concert hall where at least 80 people were killed.

In all, French authorities put the number of dead at 128, though the death toll is expected to fluctuate as the situation becomes clearer.

The threat of ISIS is well-known, with the jihadist group's atrocities in Syria and Iraq being met with condemnation and airstrikes by a U.S.-led coalition that includes France.

Hostages flee The Bataclan concert hall

Hostages flee The Bataclan concert hall 01:09
But the scale and apparent coordination of Friday's attacks inside the European Union, which comes on the heels of ISIS' claim of taking down a Russian airliner in Egypt, represent an escalation of capabilities if confirmed.


In an online statement distributed by supporters Saturday, ISIS said eight militants wearing explosive belts and armed with machine guns attacked precisely selected areas in the French capital.

A Syrian passport was found near the body of an attacker outside one of the targeted sites, the Stade de France, according to a police source, CNN affiliate France 2 and other French media reported.

A source close to the investigation told CNN that an Egyptian passport was found on another attacker. "There is strong assumption that these passports are fake," the source said.

In addition to those killed, 180 others were injured, according to the Paris Police Prefecture. More than half of them are in critical condition.

Americans are among the injured, U.S. State Department deputy spokesman Mark Toner said Saturday.

President Francois Hollande blamed the attacks on ISIS, calling it "an act of war" by the militants. He said it was planned from the outside -- "with inside complicity."

"When the terrorists are capable of doing such acts, they must know that they will face a France very determined," he said.

What we know so far about the attacks

Response in wake of attacks
Hollande issued a state of emergency as the attacks unfolded Friday.

On Saturday, French Interior Minister Bernard Cazeneuve elaborated that the state of emergency could mean restrictions on people's movements, among other measures. Border controls were tightened as of Friday, and the gendarmerie paramilitary police are on heightened alert, he said.

While ISIS claims have not been confirmed, a senior U.S. intelligence official told CNN the U.S. government has "no reason to doubt" Hollande's attribution of the attacks to the terrorist group.

The coordination and sophistication of such attacks are the most recent evidence that ISIS is eclipsing al Qaeda as the most significant global terrorist threat.

The "scale and complexity" of the Paris attacks "surprised everyone," said Peter Neumann, director of the International Centre for the Study of Radicalisation at King's College London.

Terror experts had been expecting some kind of attack but did not think ISIS capable of carrying off something on the scale of Friday's terror, he said.

One of the attackers has been identified by fingerprints as a French national known to police, a source close to the investigation of the attacks told CNN.

Airports in France remained open, and airlines were still flying there, though some airlines reported canceled flights.

Some airlines were offering refunds to passengers who decide they do not want to fly to Paris.

Night of horror
Gunmen hit Friday night when bars and restaurants were bustling with residents and tourists. When they stormed in, glass shattered under the rage of bullets. Excited weekend chatter turned into panicked screams.

May the Souls of the faithfuls departed through the mercy of God rest in peace