Ugandan rebels have killed more than 400 people in northeastern Congo since Christmas, an aid agency said Tuesday.
The Catholic charity, Caritas, cited reports by its staff in the region.
"Caritas is shocked by its staff reports of a series of massacres in the Democratic Republic of Congo carried out by Ugandan rebels on Christmas Day and the days following," the group said in a statement on its Web site.
The Lord's Resistance Army rebel group and the Ugandan government have accused each other of being behind recent attacks in the remote area, where the rebels have bases.
Patrick Nicholson, a spokesman for the Catholic charity, said the staff identified the rebels by their dreadlocked hair and their Acholi language. "There was no question in the staffs' minds that it was the LRA," he told The Associated Press in a telephone interview.
Telephone calls by the AP to the rebels were not returned Tuesday. But Uganda's army spokesman, Paddy Ankunda, said the Caritas report was accurate. Regarding the rebels, he said: "We are closing on them. We will certainly get them and stop the killings."
The allegations are the latest reports of attacks in the area near where the armies of Uganda, Sudan and Congo began an offensive this month to root out the Lord's Resistance Army.
On Monday, officials and witnesses said attackers had hacked to death scores of people who sought refuge at a Catholic church the day after Christmas, and the United Nations said the rebels had killed a total of 189 people in three villages in the area on two recent days.
The Lord's Resistance Army has waged one of Africa's longest and most brutal wars for the last two decades. In the past, aid and rights groups have accused the rebels of cutting off the lips of civilians and forcing thousands of children to serve as soldiers or sex slaves. The conflict has spilled out of northern Uganda and into Sudan and Congo.
Congo suffered back-to-back civil wars from 1996 to 2002 that drew in neighboring countries in what became a rush to plunder Congo's massive mineral wealth.
Currently, long-running peace talks between the Lord's Resistance Army and the Ugandan government have stalled. Rebel leaders have sought guarantees they will not be arrested under international warrants. The rebels' elusive leader, Joseph Kony, and other top members are wanted by the International Criminal Court in The Hague for war crimes and crimes against humanity.