KINSHASA – Militia fighters in central Democratic Republic of Congo decapitated about 40 police officers in an ambush, local officials said on Saturday, the deadliest attack on security forces since an insurrection in the region began last August.

The Kamuina Nsapu militants attacked the police on Friday as they drove from Tshikapa to Kananga. The militia members stole arms and vehicles, Francois Kalamba, speaker of the Kasai provincial assembly, told Reuters.

The insurgency, which has spread to five provinces, poses the most serious threat yet to the rule of President Joseph Kabila, whose failure to step down at the end of his constitutional mandate in December was followed by a wave of killings and lawlessness across the vast central African nation.

“They were apprehended by the militia members and they decapitated about 40,” Kalamba said, adding that the militia spared the lives of six other police officers they captured because those officers spoke the local Tshiluba language.

Corneil Mbombo, president of the Civil Society of Kasai, a province-wide activist group, also told Reuters that about 40 officers had been decapitated.

More than 400 people have been killed in the violence in central Congo, according to the United Nations, and the government said on Tuesday that 67 police officers and many soldiers had died in the clashes.