Kinshasa - The United Nations yesterday appeared powerless to stop fighting between Ugandan and Rwandan soldiers in the Democratic Republic of Congo city of Kisangani. At least 50 civilians, including 19 children, have been killed since the clashes began on Monday, observers said. The fighting broke out in Kisangani despite a UN-brokered agreement signed last month for both countries to withdraw their troops from the rebel-held north-eastern city.