U.N. officials said their investigators have yet to establish who was behind the reported killing last week of more than 900 civilians in the rebel-held northeastern Democratic Republic of Congo.
The team of investigators went to the former rebel stronghold in the Democratic Republic of Congo's Ituri district to interview more witnesses.
Officials with the U.N. Mission in Congo said they had received reports that 966 people had been killed in summary executions by what witnesses believe were ethnic militias in the town of Drodro and nearby villages.
Investigators who traveled to the area said they had seen at least 20 mass graves with blood and clothing scattered about. They also saw at least 49 survivors who were badly wounded.
U.N. workers said they had rushed about 200 kilos of basic first aid supplies to Drodro.
Residents said the attack happened last Thursday, went on for about three hours, and appeared to have been well coordinated.
It is still not clear exactly who carried out the siege, which took place in an area where two ethnic groups, the Lendus and the Hemas, have for a long time clashed, mainly over land issues. The clashes intensified since the outbreak of Congo's devastating civil war in 1998, when ethnic groups took sides among the various anti-government factions.
The spokesman for the U.N. Mission in Congo, Hamadoun Toure, told VOA that residents have provided some details that may help investigators eventually determine who was responsible.
"They did not say exactly who [they were], but they said the battalions came from five different directions, (and) that they were speaking Kilendu, which is a language spoken both by Lendus and Hemas from the north. They also said they were speaking Congolese Swahili. They were wounded by machetes and bullets. So, it seems guns were used," Mr. Toure said.
One of the rebel groups that operates in the area, the Union of Congolese Patriots accused Ugandan elements of infiltrating the militias that carried out the attack.
Uganda, which has maintained troops in Congo during the course of the civil war, has denied involvement in Thursday's killings. The Ugandan army said its troops were positioned several kilometers from the scene.
Rebel groups, the Congolese government, and political groups signed a peace agreement to end the civil war earlier last week in South Africa.