A US army Black Hawk helicopter flys over ISAF July 9, 2011 in Kabul, Afghanistan, in this file image.
Six U.S. soldiers serving with the NATO International Security Assistance Force were killed when their "Black Hawk" helicopter crashed in southern Afghanistan Tuesday, officials said. The aircraft had a hard landing due to a mechanical problem and was attacked by militants after it went down, a U.S. defense official told NBC News. NATO said the crash was under investigation and there were no reports of enemy fire in the area when it went down. NATO did not reveal nationalities of the victims. A deputy governor in the country's southern Zabul province told The Associated Press the helicopter had crashed in Afghanistan's remote Shajau district.Get More at NBC News