NATO says five people have been killed and five others injured in a helicopter crash on its base in the Afghan capital, Kabul.

In a statement Sunday, the alliance said the helicopter "crashed due to a non-hostile incident Oct. 11 at approximately 4:15 p.m. at Camp Resolute Support, Kabul."

The alliance says the incident is under investigation. The nationalities of those killed and injured were not released, according to protocol.

Earlier, U.S. Army Col. Brian Tribus, the military spokesman, said an "incident" involving a NATO aircraft and an observational balloon had taken place "in the vicinity of the Resolute Support base."

The balloon was severed from its mooring in the incident, he said, without providing further details.

An Afghan security guard said the military helicopter appeared to strike the balloon as it was landing.