BAGHDAD, Nov. 25 (Xinhua) -- Two U.S. soldiers distributing humanitarian aid were shot dead by unknown gunmen in northern Iraq on Tuesday, the U.S. military said in a statement.

    The incident took place west of the northern Iraqi city of Mosul, some 400 km north of Baghdad, as two gunmen opened fire on a group of U.S. troops distributing humanitarian aid, said the statement.

    The killed included a marine and a soldier, the statement said, adding that two other marines and three Iraqi civilians were also wounded in the attack.

    According to the military, one of the two gunmen appeared to be wearing an Iraqi uniform, but it is unknown if the attacker was an Iraqi soldier or an insurgent in disguise.

    About 4,207 U.S. soldiers have been killed in Iraq since the U.S.-led invasion in March 2003, according to media count based on Pentagon figures.