Special report: Tension escalates in Iraq  

    NAJAF, Iraq, Jan. 28 (Xinhua) -- Iraqi security forces backed by U.S. helicopters fought fierce battles Sunday with radical militant group outside the Shiite holy city of Najaf, some 160 km south of Baghdad, a police source told Xinhua.

    "The clashes erupted when the Iraqi security forces raided orchards in the Zargah area north of Najaf, but an extremist militant group based in the orchards fought them," the source said on condition of anonymity.

    Iraqi forces surrounded the orchards and were battling the militants, he said, adding that no U.S. troops were involved in the clashes, but U.S. helicopters were providing support from the air.

    The Iraqi authorities uncovered a plot by the militants to kill some Shiite clerics on Monday, the climax of the Shiite mourning ritual of Ashura which marks the anniversary for the 7th century Battle of Karbala, the source added.

    Explosions and heavy machinegun fire were heard since early morning and lasted several hours during the day while U.S. helicopters were circling above the battle area, witnesses said. They said they saw one U.S. Apache helicopter was shot down by the militants' fire and smoke was rising from a site controlled by the militants.

    However, the U.S. and Iraqi military sources did not confirm whether there was any helicopter crashed at the scene.