What are US Military Aircraft doing in Sudan?

[whell]

"KAMPALA, Uganda (AP) -- Rebel fire hit two U.S. military aircraft responding to the outbreak in violence in South Sudan on Saturday, wounding three U.S. service members and heavily damaging at least one of the aircraft, officials said. South Sudan blamed the attack on renegade troops in control of the breakaway region."

"It was not immediately known what the U.S. aircraft were doing in Bor. One official said it appeared the aircraft were Ospreys, the type of aircraft that can fly like a helicopter and a plane."

http://hosted.ap.org/dynamic/stories...12-21-07-08-38

I know that we've had operations going on there to get US citizens out of the area. But WTF were the military aircraft doing "responding to the outbreak in violence"?