A Nigerian Mi-24B attack helicopter has crashed at a military base in the country’s southern Niger Delta, but there were no immediate reports of casualties, Nigeria's Air Force says.

“A Mi-24B helicopter on a training exercise made an emergency landing today at the Nigerian Air Force Base, Port Harcourt, at about 10:00 a.m.,” the Air Force said in a statement issued on Thursday.

The cause of the crash has not been determined and an investigation is underway, the statement added.

On May 6, a Nigerian fighter jet taking part in military operations in neighboring Mali crashed reportedly due to a mechanical problem in Niger, and its two pilots were killed.

The fighter jet was part of the Nigerian air fleet attached to a West African regional force, which is participating in the French-led war against Malian fighters.

The two deaths were the first casualties in the Mali war for Nigerian troops, which form the largest contingent in the 6,000-strong African force to Mali.

France launched a war in Mali on January 11 under the pretext of halting the advance of fighters in the country.