Chances Growing Captured Islamic State Fighters Will Return to Battlefield

U.S. counterterrorism officials are increasingly worried Islamic State fighters captured as the terror group's caliphate collapsed in Syria will find their way back to the battlefield.

The concern, they say, is most acute for the approximately 2,000 foreign fighters who are being kept in a state of limbo, held in makeshift prisons run by the U.S.-backed Syrian Democratic Forces as their home countries refuse to take them back.

"We've gotten kind of fatalistic...