was able to avoid fighting on the front lines, the war was never far away.

"It was a place that was constantly being bombed," he said. "You were always on edge. Day and night, just bombs and airstrikes. You sleep in the middle of the day. I spent most of my time living in a mosque. I just remember every day hoping not to get bombed."

Clark said he crossed into Syria from Turkey in June 2015.

The Texan was detained around the same time as two foreign militants from Pakistan, a fourth from Dublin, Ireland, and fifth man from Trinidad and Tobago, according to the Kurdish-led Syrian Democratic Forces.

The State Department said it was aware of "these open source reports" but gave no further comment.

Shiraz Maher, deputy director of theInternational Centre for the Study of Radicalization and Political Violence at King's College London, said there were conflicting reports on how many foreign fighters remained in Syria.

"Some have been captured, some have been killed and some are still alive and operational," he said.

Last year, a report by the Program on Extremism found that 64 Americans had traveled to Iraq and Syria in support of the Islamic State since 2011. This compares to the thousands of Europeans who joined ISIS during the same period.

Richard Engel reported from Northern Syria, Saphora Smith reported from London and Corky Siemaszko reported from New York.