The US military aircraft were about to land in Bor, the capital of the state of Jonglei and scene of some of the nation's worst violence over the last week, when they were hit. The military said the four wounded troops were in stable condition.
"After receiving fire from the ground while approaching the site, the aircraft diverted to an airfield outside the country and aborted the mission," the statement said. "The injured troops are being treated for their wounds." It was not known how many US civilians are in Bor.
After the aircraft took incoming fire, they turned around and flew to Entebbe, Uganda. From there the service members were flown to Nairobi, Kenya aboard a US Air Force C-17 for medical treatment, the statement said.
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South Sudan's military spokesman, Col Philip Aguer, said that government troops are not in control of Bor, so the attack on the US aircraft has to be blamed on renegade soldiers.
"Bor is under the control of the forces of Riek Machar," Aguer said.
Rob McKee, operations manager for Warrior Security, a South Sudan security company, said the UN helicopter made an emergency landing while trying to evacuate personnel from a base in Yuai, Jonglei state. A second official who insisted on anonymity because the information hasn't been released said the helicopter was abandoned and remains unable to fly. No injuries were reported.