ISIS claim on Paris attack

ISIS claim

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.

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.

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.

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.

The passport belonged to a person who had been processed on the Greek island of Leros, Greek Deputy Minister of Citizen Protection Nikos Toskas said Saturday. CNN cannot independently verify that the passport was authentic or whether it actually belonged to one of the attackers.

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.

Hollande blamed the attacks on ISIS and said they were 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.

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.

Timeline of attacks

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.

What we know about the attacks