Kathmandu - Bad weather likely caused a US helicopter to crash in Nepal while on an aid mission to help victims of April's massive earthquake, killing 13 people, the United States Marine Corps said.
The UH-1Y Huey helicopter was delivering relief supplies and evacuating injured quake victims to Kathmandu when it went missing on May 12, the same day a deadly aftershock hit the Himalayan nation.
Six US Marines, two Nepalese soldiers and five villagers died in the accident, the Marine Corps said Friday in a press release summarising the results of their investigation into the crash.
After picking up injured civilians from northern Dolakha district, the crew decided to fly the most direct route to the capital, apparently to secure urgent medical aid, the investigation found.
"The chosen course required a brief period over unfamiliar terrain with unstable meteorological conditions," the Marine Corps 3rd Expeditionary Force, based on the Japanese island of Okinawa, said.
"It is believed that the aircraft... was enveloped by rapidly developing clouds or lifted into a cloud by rising air currents," it said.
"As they attempted to manoeuvre out of the weather conditions, they lost visual reference with the terrain and impacted the ground."
Relief teams from 18 nations, including India, China and the United States, spent weeks working to provide water, food, shelter and medical assistance to Nepal after a 7.8-magnitude quake struck on April 25.
The disaster killed nearly 9,000 people, destroyed more than half a million homes and left thousands without shelter just weeks before annual monsoon rains.