Congolese officials say Ugandan rebels are fleeing toward the Central African Republic in the face of a joint operation by Congo, Uganda and Sudan.

The Democratic Republic of Congo government said Friday that the rebel Lord's Resistance Army has suffered heavy losses during the coalition offensive in the northeastern Orientale province.

The Central African Republic is reinforcing its border with Congo, but did not report rebels attempting to cross on Friday.

Margarida Fawke of the U.N. refugee agency on Friday said civilians in northeast Congo are still falling victim to violence by suspected rebels.

The United Nations has called on Congo to send more troops to the area to prevent atrocities.

Refugee officials say the rebels have killed between 400 and 500 people in the province in recent days. Witnesses said the rebels massacred civilians in a church and hacked to death villagers.

The rebels have denied responsibility and blamed some recent attacks on Ugandan troops.

The Lords Resistance Army has been fighting a 20-year war against the Ugandan government, but has also become a threat in the DRC, Sudan, and the Central African Republic.

The rebel group is notorious for killing and mutilating civilians and kidnapping children for use as soldiers and sex slaves.

The International Criminal Court has indicted the group's leader, Joseph Kony, on war crimes charges. Kony has demanded the court drop its arrest warrant before he signs a peace deal his group has negotiated with the Ugandan government.

Some information for this report was provided by AFP, AP.