A U.S. citizen accused of fighting with the Islamic State says he wasn't a fighter, but was kidnapped and imprisoned by the militant group.

He's told the government he tried to escape several times and was in Syria to "understand firsthand and report" about the conflict.

New details about the unidentified detainee, held without charge in Iraq by the U.S. for nearly five months, were included in court papers the American Civil Liberties Union filed Friday in Washington. The ACLU says if the U.S. government wants to continue to detain him, it must charge him with a crime.

The government says it can hold him under war powers Congress passed after 9/11 and during the Iraq war.

The ACLU says those war powers don't apply in the battle against IS.