WASHINGTON -- The U.S. Department of Defense said Thursday that an American citizen has surrendered to the Syrian Democratic Forces and was turned over to U.S. forces.

U.S. military officials said earlier that a man believed to be an American citizen who was fighting with Islamic State of Iraq and Syria (ISIS) militants surrendered in Syria.

The Department of Defense said in a statement to CBS News that a U.S. citizen who surrendered to SDF "on or around" Sept. 12 is now "being legally detained by Department of Defense personnel as a known enemy combatant."

According to "60 Minutes," an estimated 260 Americans have joined -- or tried to join -- terrorists overseas. CBS News' Scott Pelley spoke to Abdirizak Warsame, a Minneapolis man who was sentenced to two and a half years in prison after pleading guilty to conspiring to provide material support to ISIS. Warsame said the beliefs espoused in ISIS promotional videos "kind of takes control of you."

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"You think you're doing something for a greater cause," Warsame said. "And you think you're doing it for good."

