At least 535 civilians were killed on December 16 and 17 in three villages in Yumbi.
The ethnic bloodletting went largely unnoticed at first because it coincided with the run-up to long-awaited presidential elections.
Days passed before details began to trickle out, and it took a month before the scale of the killing emerged.
Democratic Republic of Congo has acknowledged for the first time that local officials played a role in sparking the slaughter of hundreds of people last December.
At least 535 civilians were killed on December 16 and 17 in three villages in Yumbi, a remote territory in western DR Congo on the banks of the Congo River some 350 kilometres (200 miles) north of Kinshasa.
The ethnic bloodletting went largely unnoticed at first because it coincided with the run-up to long-awaited presidential elections. Days passed before details began to trickle out, and it took a month before the scale of the killing emerged.
"What happened in Yumbi in December 2018 is not a source of pride for my country," DRC Human Rights Minister Marie-Ange Mushobekwa said in Geneva on Tuesday.
"Local political and administrative actors manipulated the massacre, unfortunately leading to the nightmare we are describing today," Mushobekwa said, characterising the conflict as "essentially linked to land".
Atrocities included the killing and disembowelment of pregnant women and genital mutilation, she said.
The minister was speaking at the United Nations' human rights council following the publication of a UN investigation carried out from January 17 to 26.
Planned massacre
When AFP visited the scene in late January, local sources said the massacre had been a carefully planned attack on the Banunu community by members of the Batende ethnic group.
The attack was carried out using military-style tactics, with some assailants dressed in army uniforms, the sources said.
Some of the sources implicated members of the armed forces and the local authorities in the massacre.
After the bloodshed, the government replaced several territorial officials, including the police and intelligence chiefs, army staff and administrative personnel.
UN investigators last week said they found that the various episodes of violence, which were preceded by a dispute over the burial of a Banunu customary chief, were "strikingly similar".
Their report detailed horrific abuse, including an account of a two-year-old thrown into a septic tank, and a woman reportedly raped after her husband was killed and their three-year-old child was decapitated.
The attacks could amount to war crimes, the investigators said.
The probe said it was unable to establish any "state responsibility" for the massacre.
"However, the responsibility of the state is involved to the extent that the inquiry was able to establish that national and provincial authorities had been informed of the high risk of violence but did not take any preventive measure," it said.
Mushobekwa said that the DRC's newly elected president, Felix Tshisekedi, had ordered an investigation into what happened and its report would be sent to the UN rights panel "in the next few days."
"Those who carried out these massacres are going to be, and must be, brought to Congolese justice to reply for their acts. We are fully aware that without justice, there will be no sustainable peace in the DRC."