LAGOS, July 21 (Xinhua) -- A Nigerian Air Force helicopter has crashed in Bama area of restive northeast Nigeria's Borno State, the country's military authority said on Monday.

National defense spokesperson Chris Olukolade said the Mi-35 aircraft operated by the Nigerian Air Force was on a training mission due to technical fault when it crashed at a location south of Bama in Borno.

No casualties figure has been reported. Investigation has commenced to unravel the circumstances that led to the accident, he added, noting that the crash is not a result of any enemy action, although the military had been in a tough battle with insurgents in the area.