(Recasts, adds quotes, details, background) By Joe Bavier KINSHASA, Sept 25 (Reuters) - Six civilians were killed when Ugandan soldiers opened fire on a Congolese passenger boat on Lake Albert on Monday, in the latest border flare up between the Great Lakes neighbours, U.N. officials said on Tuesday. In a conflicting version of the shooting incident, Uganda's military reported two soldiers killed, one from each country, in what it said was a gunfight during a dispute over an oil exploration vessel working on the border lake. Ties between the two Great Lakes neighbours have been badly strained in the past by border disputes and incursions. Uganda has twice invaded Congo saying it wanted to flush out rebels, triggering a 1998-2003 war that drew in five other nations. The two countries share Lake Albert, which has become an important new frontier in the search for oil on the continent. On Aug. 3 a British contractor working for Canada's Heritage Oil Corp was killed in a clash involving troops from both states. A spokesman for the U.N. mission in Congo (MONUC) quoted witnesses as saying Monday's shooting occurred when a Ugandan patrol boat carrying troops stopped a Congolese lake passenger vessel whose occupants included two Congolese soldiers. "They (the witnesses) said they had been stopped by a UPDF (Uganda People's Defence Forces) boat with 12 to 15 soldiers on board. The UPDF told the FARDC (Congolese soldiers) to hand over their weapons. They refused and the UPDF opened fire," acting MONUC spokesman Michel Bonnardeaux told Reuters. Another U.N. source said the dead, who included two women and a child, were all civilians. Uganda's army spokesman, Major Felix Kulayigye, said Monday's violence happened after U.N. peacekeepers impounded an oil exploration vessel operated by Heritage. "When our forces went in to intervene they were countered by an armed Congolese patrol boat and fire was exchanged leaving one Congolese soldier and one on our side dead," he said. OIL INTEREST The MONUC spokesman said the U.N. peacekeepers had intercepted the Heritage vessel after it strayed into Congolese waters. But he said there was no shooting in this operation, which occurred before the passenger vessel was fired on. "As far as we know they are not related. They were reported to us as separate incidents," Bonnardeaux said. The oil vessel was escorted to Kasenye on the Congolese side and was later released after its crew were questioned, he added. Brian Westwood, the Uganda manager for Heritage, said an investigation was under way. But another company official denied the exploration vessel entered Congolese waters. "We are the only people who use GPS (global positioning system) technology on that lake. We know the borders more than anyone. Our boat was clearly in Ugandan water," the official, who declined to be named, said. Interest has been growing in the area since explorers Heritage and Tullow Oil found light crude in the Albertine Basin, which spans the border. Heritage runs two blocks in 50-50 partnership with Tullow and between them they have drilled six wells, all yielding high quality crude. They estimate reserves of up to a billion barrels. Following the death of the Heritage contractor in August, Kinshasa accused the company of prospecting illegally in its waters. Heritage, and Uganda's government, denied it. On Sept. 8, Ugandan President Yoweri Museveni and his Congolese counterpart Joseph Kabila met in northern Tanzania and agreed to do more to rid their countries of rebels blamed for destabilising eastern Congo. They also agreed to collectively explore and use any oil found on the border. (Additional reporting by Francis Kwera in Kampala)
