US Marine Corps Major Adrian Rankine-Galloway told the news station the citizen was 'legally detained by Department of Defense personnel as a known enemy combatant, ' while it's unclear how long the individual was involved in the ploy.
As to when and where the surrender took place was not immediately made clear.
The individual, who surrendered to Syrian Democratic Forces (SDF) on or around September 12th, has since been turned over to US forces, said Eric Pahon, Department of Defense spokesperson.
The report was also confirmed to CNN by an unnamed U.S. military official.
On the campaign trail, Trump indicated he was open to detaining USA citizens at Guantánamo Bay and trying them at the military commissions there.
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In the statement, the command said foreign fighters who are captured or surrender to SDF partners in Syria will be safeguarded and transported humanely.
A U.S. citizen fighting alongside Islamic State terror group militants in Syria has been captured, the Daily Beast reported Thursday.
On Thursday, the chief spokesman for the United States military command referred all questions about the news.
"According to CNN, a U.S. military official told the outlet that the American citizen surrendered to the Kurdish elements of the Syrian Democratic Forces".
The American fighter, whose identity was not released, is not the first American ISIS fighter captured on the battlefield. The Islamist militant group had taken control of large parts of the two Middle East nations in 2014 to establish an Islamic caliphate, but they have been driven out of their strongholds in both the countries following months long offensive launched by local forces and an anti-Isis US-led coalition group. He later expressed regret in a television interview.