The Ugandan army ordered rebel fighters out of the northeast Congolese town of Bunia today following clashes that killed over 90.
Many of those killed were women and children who were hacked to death.
United Nations observers said the Ugandan army had told fighters of the Congolese Union Party (UPC) to get out of Bunia, which had been under the control of a Ugandan-backed rebel faction before fighting erupted last week.
"We hope they comply," a UN mission spokesman in the Democratic Republic of the Congo's capital, Kinshasa, said.
United Nations observers, who have no weapons to intervene in fighting, found two mass graves in Bunia containing 75 mutilated bodies last week and 15 more corpses on Sunday.
The fighting, triggered by a tribal war, has underlined the difficulty of ending the messy conflict in Africa's third biggest country and getting foreign armies home after four years of war that have killed an estimated two million lives.