WASHINGTON (REUTERS) - An American citizen fighting for Islamic State in Syria surrendered to US-backed fighters earlier this week and has been handed over to US forces, the Pentagon said on Thursday (Sept 14).

The American surrendered to the Syrian Democratic Forces (SDF), a US-backed alliance of mostly Arab and Kurdish fighters, on or around Sept 12.

"The US citizen is being legally detained by Department of Defense personnel as a known enemy combatant," Pentagon spokesman Major Adrian Rankine-Galloway said in a statement.

It is not the first time an American citizen fighting for the group has been detained by US allies.

In June, a Virginia man who travelled to Syria to become a suicide bomber for Islamic State in Iraq and Syria (ISIS) was convicted of providing material support to the militant group.

Mohamad Jamal Khweis, 27, spent about two and a half months in early 2016 travelling with ISIS fighters in Syria and Iraq and participating in the group's religious training.

He was detained by Kurdish peshmerga forces in northern Iraq in March 2016 and turned over to US authorities.