The U.S. military said an Iraqi soldier has been killed when two U.S. helicopters collided while landing at a base in Baghdad, AP reported. A statement says two American troops and two other Iraqis also were wounded when the UH-60 Black Hawks crashed at about 8:55 p.m. in a northern section of the capital. Military spokesman Capt. Charles Calio said it's not clear how severe the collision was but it did not appear to be caused by hostile fire. The military said it's not known yet how many people were on board the aircraft and an investigation is under way.