WASHINGTON (AP) — Iran has entered the fight to retake a major Iraqi oil refinery from Islamic State militants, contributing small numbers of troops —some are operating artillery and other heavy weapons — in support of advancing Iraqi ground forces, U.S. defense officials say. Two U.S. defense officials said Iranian forces have taken a significant offensive role in the Beiji operation in recent days, in conjunction with Iraqi Shiite militia. The Iranian role was not mentioned in a new U.S.