The capture of five foreign fighters, including two Americans, by U.S.-backed forces battling Islamic State in Syria is spotlighting a long-simmering problem: Countries are largely refusing to repatriate hundreds of such militants held there.
The Syrian Democratic Forces on Sunday said they captured the foreign fighters as part of a monthslong campaign backed by U.S.-led coalition airstrikes to defeat the militant group in its last territorial pocket in Syria’s east. One of the Americans came from Texas and applied to become...