The UN Human Rights Council chief called for an independent, international probe into the "horrific attacks" allegedly carried out by Bana Mura militia against civilians.
The UN rights chief on Tuesday accused authorities in the Democratic Republic of Congo of backing a new militia behind "horrific attacks" in the Kasai provinces, including killing and mutilating hundreds of civilians.
"I am appalled by the creation and arming of a militia, the Bana Mura, allegedly to support the authorities in fighting the Kamwina Nsapu (rebels)," Zeid Ra'ad Al Hussein told the UN Human Rights Council.
Over the past two months, the militia had carried out "horrific attacks against civilians from the Luba and Lulua ethnic groups."
The militia destroyed entire villages, and shot, burned and hacked to death villagers, among them babies and young children.
Since last September, the armed followers of tribal chieftain Kamwina Nsapu — who was killed a month earlier — have rebelled against the authority of the central government.
Over 3,000 dead
Figures collated by the Roman Catholic church in a report dated June 19 show violence in the Kasai region has killed more than 3,300 people in eight months. This figure is far higher than the "more than 400 dead" given by the UN peacekeeping mission in April.
On Tuesday, Zeid accused "various actors" in the conflict of "fuelling ethnic hatred, resulting in extremely grave, widespread and apparently planned attacks against the civilian population in the Kasais."
He called for an "independent, international investigation" to be set up to probe the situation in the region.
The Human Rights Council is due to vote later this week on a resolution tabled by the European Union and backed Tuesday by a number of countries including the US to create such a probe.
TRT World's Fidelis Mbah has more on the report.
Zeid said he had already deployed a team of investigators to interview refugees from the region and had been horrified by what they learned.
In one case, a "well-known" local leader reportedly provided machetes, hunting rifles and fuel to Bana Mura militia members for their attack on the village of Cinq on April 24.
Dozens of men, women and children were reportedly shot, hacked or burned to death in the attack, Zeid said.
"Hundreds of assailants also allegedly attacked the main health centre in the village and killed some 90 patients, medical personnel and others," he said.
More than 20 other villages had faced similar attacks, he added.
Victims and witnesses had repeatedly said local authorities, and in some cases "state agents" and members of local units of the national army and police forces, had armed and organised the militia.
Zeid stressed that the Kamwina Nsapu were also accused of committing serious abuses, including targeted killings and using child soldiers as young as seven.