SULAIMANIYA, Iraq — Before dawn on Monday, Kurdish soldiers noticed a man approaching them near the ancient city of Sinjar, the site of violent clashes with Islamic State fighters. The soldiers sounded an alarm, warning of a possible suicide bomber. But the man soon called out in a mixture of broken Arabic and perfect English that he wanted to surrender.

He was unarmed and was carrying three cellphones, said Sarbaz Hama Ameen, a Kurdish pesh merga officer who was present. He also had a few thousand dollars in mixed currency and, most surprising, a Virginia driver’s license.

Within hours, the American authorities were investigating how a young man from the Washington suburbs ended up in northern Iraq, near the border with Syria, in the midst of the bloody war with the Islamic State. The F.B.I was trying to piece together his travels and figure out what drew him there.

Image A photograph on social media shows a man the Kurdish military says is an American who turned himself in on Monday. Credit... via Associated Press

Little was certain, including the man’s identity. Kurdish officials originally released one name, then circulated the driver’s license bearing a different one: Mohamad Jamal Khweis, 26. In Alexandria, Va., at the address on the license, a man identified as Mr. Khweis’s father alternated between defending his son to reporters, denying he was his father and making threats.