A U.N. peacekeeper was shot dead and two others were injured Friday by unidentified gunmen in Sudan's state of East Darfur, the United Nations said. According to AP, the slain man was Nigerian, the U.N. spokesman's office said. The United Nations says it is working with Sudan's government to investigate the attack on the peacekeeping team's site near Muhajeria in East Darfur State. An estimated 18,000 displaced persons remain concentrated around the U.N. team sites near Muhajeria and Labado villages since April 6, when fighting broke out between Sudanese government forces and the Sudan Liberation Movement/Minni Minawi, the U.N. said. Secretary-General Ban Ki-moon was "appalled and saddened" by the killing, his spokesman's office said.