In a turbulent state, a Nigerian military chopper crashes.

A Nigerian military helicopter has crashed in Kaduna, the country's northernmost metropolis.

Two pilots were on board the training plane when it crashed on Tuesday evening, according to military sources.

The cause of the crash is still unknown, as is the fate of the pilots.

Hundreds of people have been killed and thousands have been forced to flee their homes as a result of armed gang attacks in Kaduna state.

Kidnapping for ransom has become all too regular in the state.

At least four Nigerian military planes have been involved in fatal crashes in the last year, including one that killed the country's army chief and a dozen other soldiers.

Details of past accident investigations have not been made public by the authorities.