"A US Air Force CV-22 Osprey crashed in southern Afghanistan late last night, killing three US service members, one civilian employee, and injuring numerous other service members," the alliance said.
The helicopter came down 11 kilometres west of Qalat in volatile southern Afghanistan's Zabul province on Thursday night.
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The cause of the crash remains unclear: Taliban fighters claim to have shot the helicopter down, but an Afghan official insists mechanical failure was to blame.
Cause of deadly crash unclear
Taliban insurgents have a history of false and exaggerated claims designed to promote their cause of driving foreign forces from the country.
Choppers are used extensively by both NATO and Afghan government forces to transport and supply troops spread out across a mountainous country with few roads.
Losses have been relatively light, despite insurgent fire and difficult conditions and most crashes have been accidents caused by maintenance problems or factors such as dust.
Lacking shoulder-fired missiles and other anti-aircraft weapons, the Taliban rely mainly on machine guns and rocket propelled grenades to target helicopters at their most vulnerable during landings and takeoffs.
One of the heaviest single-day losses of life for allied forces occurred on June 28, 2005, when 16 US troops died aboard a Special Forces MH-47 Chinook helicopter that was shot down by insurgents.
