Jean-Pierre Bemba, who heads the Congo Liberation Movement, told Reuters news agency that the attacks began on Friday when Angolan and Zimbabwean troops started moving east from Lisala on the Congo River, 1,000km northeast of the capital, Kinshasa.

It is the first report of fighting in northwestern Congo involving troops from Angola and Zimbabwe, who intervened against the rebels in support of President Kabila in August.

President Kabila has the support of some neighbouring countries

"There is now heavy combat. They are using heavy artillery, mortars and cannons," Mr Bemba said, speaking by satellite telephone from Mindembo, around 60km east of Lisala.

"They (the government army) have reinforcements from Angola and Zimbabwe and they started to attack us on Friday morning," he said.

He added that the fighting had continued through the night.

Extending pressure

Some three weeks ago, the rebels deployed troops to Moba to put pressure on the Zimbabwean forces further to the north in Katanga province. They claimed the capture of the town after 24 hours.

Heavy fighting has been reported from the area since then.

On Saturday, one independent source citing reports from Red Cross workers was quoted as saying that Zimbabwean and government forces had recaptured Moba on Thursday, killing more than 1,000 rebels.

The Red Cross in Kinshasa could not immediately confirm the toll.

Jean-Pierre Ondekane, the military leader of the main rebel Congolese Rally for Democracy, said that 80 government soldiers had also been killed in fighting on Thursday and Friday between Pepa and Moba, around 1,600 km (1,000 miles) southeast of Kinshasa.

On Friday, the rebels also reported heavy fighting against government troops and Zimbabweans in the southern region of Katanga.

Zimbabwe, Angola, Namibia and Chad have deployed troops in the Congo to back President Laurent Kabila against the rebels, who launched their uprising on 2 August, backed by Rwanda and Uganda.

Despite a peace agreement between Kabila, his foreign supporters and Uganda and Rwanda announced by UN Secretary-General Kofi Annan and French President Jacques Chirac in Paris last weekend, the warring sides have played down the significance of the deal.