The unit involved is responsible for transporting food, water and fuel for US-led forces, a top US official said.
Up to 19 soldiers from the unit based near Talil in southern Iraq allegedly failed to carry out their orders.
The news came amid reports that UK troops could be sent to back up the US in some of Iraq’s most volatile areas.
It is believed the troops could be sent from Basra in southern Iraq to an area south of Baghdad, and might – controversially – be under US command.
