United Nations investigators have found 17 new mass graves in the Democratic Republic of Congo (DRC), in an area that has seen fighting between soldiers and members of a local armed group, according to the UN rights chief.
Zeid Raad Al Hussein, the UN high commissioner for human rights, called the DRC's government to launch an investigation, threatening that the International Criminal Court (ICC) would do so if authorities failed to take action.
Zeid said in a statement published by his office on Wednesday that he had reports DRC soldiers had dug the graves after clashes with the Kamuina Nsapu militia in the central Kasai region in March.
"At least 74 people, including 30 children, were reported to have been killed by soldiers," in the clashes, he said, without giving details on the sources of his information.
During a separate incident in the provincial capital of Kananga last month, soldiers were reported to have shot dead at least 40 people and raped women and girls, Zeid said, again without saying who had made the reports.
Most of the victims were said to have been killed in their homes as soldiers went door to door looking for militia members, he added.
Fifteen of the newly-confirmed sites are in the town of Tshimbulu, and two in Thsienke, a village near Kananga city.
The findings mean that the UN has now documented 40 mass grave sites and killings of more than 400 people in Kasai Central and Kasai Oriental provinces since last August.
"It is absolutely vital that the government ... takes meaningful steps to ensure that there is [an]... independent investigation," Zeid said.
"Should there be no effective national investigation, I will not hesitate to urge ... an investigation by an international mechanism, including the International Criminal Court."
The government of the DRC said it would investigate the reports once it saw the evidence.
Lambert Mende, the government spokesman, said the UN team should pass its evidence to the justice department.
"Then we will start investigations," he added.
The government has previously denied that soldiers have used disproportionate force against militia members, who are often armed with machetes and home-made rifles, and said that the militia had dug other mass graves.
Kasai is the focus of the fight against the Kamuina Nsapu militia since August, when security forces killed its leader. The militia has been fighting largely to avenge his death.
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 has stoked lawlessness across the vast central African nation.
The government said last week that it had returned the body of the armed group's leader to his village, which had been one of the militia's key demands.
However, it was unclear whether this gesture would sooth tensions after such extensive killings.
The Kamwina Nsapu have been accused of recruiting child soldiers, and of attacking public authorities, schools and churches.
Hundreds of people have been killed and 200,000 displaced, according to the UN.