4 U.S. service members wounded on South Sudan flight [UPDATE] KAMPALA, Uganda, Dec. 21 (UPI) -- Three U.S. planes trying to evacuate refugees from South Sudan to Uganda were fired on Saturday, injuring four U.S. service members, the U.S. military says. One of the U.S. service members was wounded seriously. The New York Times said the aircraft were forced to return to Uganda without completing their mission. U.S. President Obama said Thursday he was sending 45 U.S. service members to South Sudan to "support the security of U.S. personnel and our embassy." Previous evacuation flights had been organized in Juba, the South Sudanese capital, but the mission Saturday apparently was the first into rebel-held territory, the Times said. The three aircraft were CV-22 Ospreys, tilt-rotor craft that can fly like a plane and land like a helicopter, to evacuate U.S. citizens from a U.N. compound in Bor, the capital of Jonglei State, the report said. The Times said the seriously wounded U.S. service member was flown to Nairobi, Kenya, where he was in surgery Saturday night. Bor is occupied by forces loyal to former vice president Riek Machar, who was dismissed from office in July, the BBC said.