The report by the UN Joint Human Rights Office in Congo (UNJHRO) is the first time the United Nations has directly suggested that government forces dug the graves.

Congo's human rights minister was not immediately available for comment but the government has repeatedly denied its troops were responsible for dozens of mass graves discovered since the Kamuina Nsapu militia launched an insurrection last August and called for the departure of government forces from the area.

"As of June 30, 2017, UNJHRO had identified a total of 42 mass graves in these three provinces (of Kasai), most of which would have been dug by (Congolese army) elements following clashes with presumed militia members," the report said.

Earlier this month, the UNJHRO said it had identified 38 more probable mass graves in the western part of Kasai, bringing the total number to 80.

More than 3,000 people have been killed and 1.4 million displaced in the violence, part of growing unrest in the country since President Joseph Kabila refused to step down when his mandate expired in December.

The violence has triggered fears of a wider conflict in the large central African country, a tinderbox of ethnic rivalry and competing claims over mineral resources. Millions died in civil wars between 1996-2003, mostly from hunger and disease.

The government has blamed the militia for the mass graves and also claimed that some of the sites identified by UN investigators have turned out not to contain bodies.

It also denies UN allegations that its troops have systematically used excessive force, although a court convicted seven soldiers this month for murdering suspected militia members in a massacre that was caught on video.

Last month, the UN Human Rights Council approved an international inquiry into the violence in Kasai. The UN High Commissioner for Human Rights is expected soon to name a team of experts to lead the probe.