Eventual victory against the Islamic State could well lead to an uptick of terrorist attacks in the West, not a reduction in them, James B. Comey, the director of the F.B.I., said on Wednesday.

“At some point there is going to be a terrorist diaspora out of Syria like we’ve never seen before,” Mr. Comey said at a cybersecurity conference at Fordham University. “Not all of the Islamic State killers are going to die on the battlefield.”

Image James B. Comey, the director of the F.B.I., warned of a potential uptick in terrorist attacks with the eventual defeat of the Islamic State. Credit... Bebeto Matthews/Associated Press

Mr. Comey predicted that the military coalition would eventually succeed in crushing the Islamic State, but that “through the fingers of that crush are going to come hundreds of really dangerous people and they are going to flow primarily to Western Europe.” But some, he said, could well end up in the United States.