It was not immediately clear where the American had been detained but it had been rumored in the first days of Turkey’s incursion against Kurdish forces in northeastern Syria that an American fighter had been captured. Turkish officials denied any knowledge of such a capture at the time.

The Turkish Interior Ministry identified the American who was deported on Monday as an Islamic State fighter.

The Turkish news media reported that the American was deported at the land crossing into Greece, but that the Greek immigration authorities refused him entry and sent him back to Turkey.

The Turkish authorities refused to let him re-enter the country and the American was photographed stranded in the buffer zone between the two borders.

A State Department spokesperson said only that the United States was “aware of reports of the detainment of a U.S. citizen by Turkish authorities. Due to privacy considerations, we have no further comment.”