A Congolese rebel leader yesterday said his forces had killed at least 800 government soldiers when they ambushed and sank two river gunboats.
Mr Jean-Pierre Bemba, leader of the Congolese Liberation Movement (MLC), said his forces "burned and sank" two gunboats mounted with heavy artillery on Thursday, on the Ubangi river in the north-west of the Democratic Republic of the Congo.
"The boats were set alight and sunk, one of them completely exploded. We have counted at least 800 bodies floating in the river. It was a massacre," Mr Bemba said. But an official from President Laurent Kabila's government dismissed the claims as false and said a government offensive against Mr Bemba's troops had been successfully completed.
The MLC, backed by the Ugandan army, is one of three rebel groups fighting to oust President Kabila, and controls most of north Congo.
Rwanda and Uganda back the two other rebel factions which have captured a vast swathe of eastern Congo since they took up arms in August 1998.
Mr Bemba said most of the government's 10th Brigade had been put out of action - hundreds had run across the border to the neighbouring Congo Republic, while others were emerging from the bush and surrendering to the rebels "every hour".
"They are in complete disarray. They are running around like fools in the bush, but we are pursuing them as they run," Mr Bemba said.
All sides in Congo's civil war last year signed a ceasefire accord in the Zambian capital Lusaka. But repeated violations have prevented the deployment of a promised 5,000-strong UN peacekeeping mission.
"We don't have any people in the area to say exactly what happened or to report on casualties," UN military observer Lieut Col Regis Barman said. "But we understand there was a big battle."
Lieut Col Barman said fighting had been going on for several weeks in the north-west, mainly along the Ubangi river between the towns of Libenge and Imese, 500 miles north of Kinshasa.
"As far as we know, there was a [government] offensive by boat and air and infantry," he said. "But the rebels seemed to halt it and now Kabila says the operation has finished."
Congolese Col David Kokolo told state television yesterday that the operation did not violate the ceasefire because it was aimed only at recovering positions captured by the MLC after the deal was signed.
The fighting has driven tens of thousands of civilians across the border to the Congo Republic and some 6,000 people to the Central African Republic to the north, said Mr Paul Stromberg of the UN's refugee agency UNHCR in Nairobi.
President Kabila's troops captured Imese last month, and Mr Bemba yesterday gave government forces a three-day ultimatum to leave the town or risk a full-scale battle.
"If they don't get out by Monday, then we will destroy the remaining troops he has," Mr Bemba said.