Rwandan Spokesman Col Wilson Rutayisire: "Indisciplined Ugandan forces are to blame"

Rwandan leader Pasteur Bizimungu flew to Kampala to try to resolve the issue as troops battled for a third day in the strategic Congolese city of Kisangani.

The Rwandans are said to control most of the town centre, while the Ugandans are reported to be in command of the road to the airport.

Uganda's Defence Minister Steven Kavuma: "The Rwandan Patriotic Army started it"

Doctors have been quoted as saying that up to 50 civilians had been killed in parts of the city which had come under artillery fire, but this casualty figure cannot be independently confirmed.

A senior American envoy, Gayle Smith, has been sent to the region.

'Battle for influence'

The two countries fought alongside the Congolese rebels in the year-long war against President Laurent Kabila.

(Click here to see a map of the region)

They both signed a peace agreement with President Kabila last month, but differences emerged over how they should end the fighting and when to withdraw their troops.

The deterioration in relations is linked to a split in the main Congolese rebel movement, the Congolese Rally for Democracy (RCD).

Uganda and Rwanda support opposing RCD factions, who each demand the right to sign the peace agreement so they can represent the rebels at a proposed national dialogue on the future of the country.

The BBC East Africa Correspondent, Cathy Jenkins, says Uganda and Rwanda are battling over the degree of influence they will be able to exert over the dialogue.

Clashes spread

Fighting broke out on Saturday and spread from the airport to the centre of the city.

African analyst Vincent Mugombe; "A row has been simmering between Rwanda and Uganda"

Reports of the clashes suggest the confrontation is far more serious than anticipated.

Rwandan commanders say Ugandan troops stationed at Kisangani's main airport opened fire on Rwandan positions a short distance away on Saturday night.

The Rwandan troops returned fire, and are said to have wounded several Ugandan soldiers.

The Rwandans accused Uganda of provoking an incident in an attempt to secure control of the airport, 25km (15 miles) east of the city, where supplies are flown in daily.

"The Ugandan army deployed troops all night to surround the airport, and they tried to block us in, they fired and there was a skirmish," said Rwandan Government spokesman Lieutenant Colonel Wilson Rutayisire.

"The Ugandan army then rallied again, directly attacking our troops, but we pushed them back," he said.

Rival factions

The RCD split in May, when Ernest Wamba dia Wamba was ousted as head of the group.

He refused to step down and, with Ugandan backing, established new headquarters in Kisangani.

Ugandan forces have been flying in troops to bolster him and his supporters.

The RCD's dominant faction, backed by Rwanda and headed by Mr Wamba's successor Emile Ilunga, is based in Goma, in eastern Congo.

A senior military commander from Dr Ilunga's wing of the RCD told the BBC that all Ugandan troops would have to leave Kisangani as soon as possible, if calm was to be restored.

But a spokesman from Professor Wamba dia Wamba's faction accused the Rwandans of trying to provoke a confrontation in Kisangani and hijacking the rebellion for their own ends.

Ministers in Kigali have expressed bewilderment and frustration at the rebel in-fighting, saying it is a serious error of judgment at best.