New Delhi, India -- An Indian Air Force helicopter crashed Friday in a mountainous region bordering Tibet, killing all 12 people on board, authorities in New Delhi said.

The MI-17 helicopter went down at 12.05 p.m. local time in Arunachal Pradesh while flying to neighboring Assam state, Air Force spokesman T.K. Singha said.

Indian military authorities have ordered an inquiry to determine the cause, he said. The helicopter was carrying Air Force crew and other military personnel when it crashed, Singha said.

India and China have a decades-old border dispute over the region of Arunachal Pradesh.

China lays claim to 34,750 square miles (90,000 square km) of land in that Himalayan territory governed by India. Both neighbors fought a brief but bitter border war in 1962.