A 16-year-old American boy fighting on behalf of the Islamic State was captured on the battlefield in Syria, an American-backed force fighting the militants said Wednesday.

If the teenager is proved to be a United States citizen, he would be the first American minor to be caught fighting on behalf of the terrorist group overseas.

His arrest follows the capture of Warren Christopher Clark, 34, a former substitute teacher from Texas whose seizure in the same area was announced on Sunday. They are among the handful of American citizens — just five so far — who have been taken alive on the front line in the battle against the Islamic State, according to a database maintained by the Program on Extremism at George Washington University.

The militia that announced the boy’s capture, the Syrian Democratic Forces, said he was among eight foreign fighters who were apprehended this week in the last sliver of Islamic State-held territory in northeastern Syria. The others included citizens of Germany, Russia, Ukraine, Tajikistan, Kazakhstan and Uzbekistan.