Fighting has broken out in Bunia, north-eastern Democratic Republic of Congo, near where a massacre of hundreds of people recently took place.
Some 1,000 people may have died in a three hour killing spree
The head of the Ugandan troops in Ituri region said the fighting erupted after they attempted to intercept hundreds of Ngiti tribesmen who raided Bunia's abattoir, the Associated Press news agency said.
"These cattle thieves usually attack outlying villages in large numbers... But this is the first time they dared come to town," said General Kale Kaihura.
The province has been beset by fighting resulting from ethnic rivalries which have claimed the lives of 50,000 people since 1999 and caused 500,000 residents to flee, human rights group Amnesty International says.
The Ituri Pacification Commission established as part of wider peace agreements to end the country's four year civil war is currently holding meetings in Bunia.
But on Thursday hundreds of people were reported to have fled the town as Ugandan troops used mortars, armoured personnel carriers and small arms against the tribesmen.
DR CONGO'S WAR
Seven foreign armies
At least 2 million dead
Disease and abuses widespread
Uganda's President Yoweri Museveni has agreed that Ugandan troops will leave by 24 April.
Last week, the United Nations received reports of a massacre of some 1,000 people from the Hema ethnic group, carried out by Lendu tribal militias, on 3 April in 14 villages around Drodro, 80 kilometres from Bunia.
Earlier this week, a senior UN official appeared to substantially revise downwards the massacre toll figure.
But a UN spokesman in Kinshasa said on Thursday they would not have accurate details about the massacres until they heard from a team, including medical officials, which was being sent next week to examine in detail the sites of the mass graves.