WASHINGTON: The Pentagon has said there are some Shiite fighters at an Iraqi military base where Washington just sent 450 reinforcements, but they were not working with U.S. forces, underscoring concerns over links with the sectarian fighters.

Pentagon spokesman Col. Steve Warren said late Tuesday that while there is a “small group” of Shiite fighters at the Taqaddum base, they numbered only in the lower double digits, did not form full units and did not interact with U.S. forces. He appeared to be responding to a media report alleging that U.S. and Iraqi personnel were “sharing” the base.

Taqaddum is a key area in the fight to retake the city of Ramadi and Anbar province from ISIS.

Shiite and Kurdish fighters have been critical in bolstering a weakened Iraqi military in efforts to fight ISIS but the United States is hesitant to see Shiite militias involved in its efforts to battle the group, despite their battle readiness.

Warren said the Shiite fighters are coordinating with Iraq government forces at the strategic base, and that the U.S. made it a condition of troop deployment to the air base that Shiite militia units be withdrawn.

“There were Shia [Shiite] militia units on Taqaddum at one point,” he added. But “one of the conditions for our arrival there was that these units move off Taqaddum air base.”

Iraqi forces have made gains in Diyala and Salahuddin provinces north of Baghdad, but much of the west is still in ISIS hands.