Iraqi soldiers train with members of the U.S. Army 3rd Brigade Combat Team, 82nd Airborne Division, at Camp Taji, Iraq, in this U.S. Army photo released June 2, 2015. REUTERS/U.S. Army/Sgt. Cody Quinn/Handout

BAGHDAD (Reuters) - An Iranian-backed militia said on Monday it said it would treat U.S. Marines deployed in Iraq to fight Islamic State as forces of occupation and "deal" with the foreign troops.

Washington said on Sunday a detachment of the 26th Marine Expeditionary Unit was in Iraq, bolstering efforts by the United States and a coalition of allies against Islamic State.

"If the U.S. administration doesn't withdraw its forces immediately, we will deal with them as forces of occupation," the Asaib Ahl al-Haq militia said on its TV channel, al-Ahd.

"The forces of occupation are making a new suspicious attempt to restore their presence in the country under the pretext of fighting their own creation, Daesh," the Shi'ite Muslim militia added, referring to an acronym for Islamic State, a ultra-hardline Sunni Muslim movement.

(Reporting by Maher Chmaytelli; Editing by Andrew Heavens)