A U.N. official says 58 people were killed in an attack on a U.N. base in South Sudan and about 100 were injured. The U.N. said an angry mob of South Sudanese youths attacked the U.N. peacekeeping mission's camp in Bor in Jonglei state on Thursday. Some 5,000 ethnic Nuers have sought safety in the U.N. base since fighting broke out in the country in mid-December. The U.N. official, speaking on condition of anonymity ahead of a formal announcement, said Friday most of the 58 people killed were Nuer but there were also casualties on the other side. The official said a surgical team from Doctors Without Borders flew into Bor to help treat the injured, including two U.N. peacekeepers. The U.N. has reinforced security at Bor, the official said.