The man, who holds dual U.S.-Saudi citizenship and whose name has not been released, was captured in September in Syria by the U.S.-backed Syrian Democratic Forces, an alliance of militias fighting against Islamic State, before being handed over to the United States.
He was then held in Iraq without legal representation until the American Civil Liberties Union intervened on his behalf in U.S. federal court last October.
“The government has effectively admitted that it has no reason to continue detaining our client and that he does not pose a threat,” said ACLU attorney Jonathan Hafetz in a statement.
“But, instead of offering a safe release, they want to dump an American citizen onto the side of the road in a war-torn country without any assurances of protection and no identification.”
The United States previously said it had evidence that he had signed up as an Islamic State foreign fighter in 2014 and entered Syria in January 2015, according to court papers. The detainee, who has a degree in electrical engineering, is married with one child, according to court papers.
The administration had previously sought to transfer the man to an unidentified country, possibly Saudi Arabia.
In its notice filed to a Washington D.C. court on Wednesday, the Justice Department said it offered the man a choice of being released “either in a town or outside an Internally Displaced Person camp,” but he would not agree to release options.
The Justice Department said it would release him in the unspecified town “no sooner than 72 hours hence.”