Members of the Kamwina Nsapu militia staged the attack on the police between the cities of Tshikapa and Kananga

Forty-two policemen have been decapitated after being ambushed by a militia group in Congo, officials report.

The officers were attacked in Central Kasai province, which has seen a spike in deadly violence in recent months.

Kasai Assembly President Francois Kalamba said on Saturday that members of the Kamwina Nsapu militia staged Friday's attack between the cities of Tshikapa and Kananga.

Kalamba says the militia members freed six policemen because they spoke the local Tshiluba language.

The Kamwina Nsapu militia has been fighting Congolese forces since August, when security forces killed their leader.

The violence has left 400 people dead. The UN and rights groups have warned Congo's military against excessive use of force.

Kasai Governor Alexis Nkande Myopompa said investigations are under way into the decapitations.

AP