Human rights spokeswoman says death toll suggests ‘disproportionate’ force with at least 39 women among victims.
The UN’s DR Congo mission said in a statement on Wednesday that the clashes took place in the central region, east of the Kasai capital, Tshikapa.
Violence between members of the Lulua-Luba and Chowe-Pende communities escalated, and saw at least 20 members of the Chowe-Pende killed, the agency said.
The Chowe-Pende accuse the Lulua-Luba of supporting the Kamwina Nsapu militia.
The Kamwina Nsapu militia claim its authority from chief Kamwina Nsapu, who was killed in the region in August 2016 by police after a rebellion against the Congolese authorities.
The militia has been fighting security forces largely to avenge the chief’s death.
According to the UN, fighting has killed at least 400 people, including two UN investigators, since government troops killed the chief eight months ago.
The violence has become the most serious threat to President Joseph Kabila, whose decision to stay in power after his mandate ran out in December gave rise to nationwide lawlessness.
The UN has accused the Kamwina Nsapu rebellion of numerous atrocities and of recruiting children for combat.
Numerous mass graves, reportedly dug by DRC soldiers after clashes with the militia, have also been found in the Kasai region.
The UN has almost 19,000 troops deployed in Congo, its largest and costliest peacekeeping mission.