The UN mission in South Sudan says one of its helicopters has crashed, and a UN official told The Associated Press that it appears the aircraft was shot down.
The UN mission said on Twitter that an Mi-18 cargo helicopter crashed Tuesday near Bentiu, which is hotly contested between the government and rebels.
The UN said it is deeply concerned about the fate of its crew.
A search and rescue team has been sent to the crash site.
The UN official, who insisted on anonymity because he was not authorized to speak to the press, said contact with the helicopter was lost at about 3:19 pm and that it was apparently shot down near Bentiu.
South Sudan has seen widespread massive violence between rebels and the national army since December.