Islamic State of Iraq and Syria

David Bowdich of the FBI's Los Angeles office said at a news conference that "there's a number of pieces of evidence that has pushed us off the cliff."

A new report glimpses life "inside the bubble of American ISIS sympathizers, a diverse and diffuse scene that the FBI estimates include hundreds, if not thousands, of individuals."

Ahmet Dahmani, 26, was arrested at a luxury hotel. Turkish police say two Syrian men were also arrested nearby, with fake passports in their possession.

The attack would be the most sophisticated yet by ISIS, as the simultaneous assaults occurred at multiple locations during a busy time of day in a major European capital.

"We know for a fact that the weapons system hit its intended target," Col. Steve Warren says. He adds that it will take time to make a formal declaration that the ISIS frontman was killed.

A force of some 7,000 Kurds says it has wrested control of Sinjar from ISIS, ending in a few days an occupation that had lasted 15 months.

The small force will be sent to northern Syria to "help coordinate local ground forces and Coalition efforts" to counter ISIS, a senior administration official confirms to NPR's Scott Horsley.

But the president warned that the campaign against the group that controls large parts of Syria and Iraq "will not be quick."

Police have arrested one suspect over the attack, which also included an explosion at the facility operated by Air Products, an American company.

Both the United Nations and the Taliban have condemned the attack, which targeted civilians who were in a long line at a bank.