There are fears that a UN helicopter has been shot down over South Sudan

A rebel commander shot down a UN helicopter in rural South Sudan, said a government spokesman.

The UN has confirmed the crash of one of its helicopters and said it was investigating the cause.

The UN mission said on Twitter that an Mi-8 cargo helicopter crashed near Bentiu, which is hotly contested between the government and rebel fighters.

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, it said.

Contact with the helicopter was lost at about 3:19pm local time and it was apparently shot down near Bentiu, said a UN official.

A South Sudan government spokesman blamed the rebels for shooting down the helicopter. Rebel commander Peter Gadet was responsible for shooting down the helicopter with a rocket-propelled grenade, said Akol Ayom Wek, the press secretary for the governor of Northern Bahr el-Ghazal state, a region loyal to President Salva Kiir.

The UN search and rescue team found three dead at the crash site, said Mr Wek. One person survived, he said. The UN had not yet confirmed any deaths or the number of people on board the helicopter.

Gadet warned the UN last week that he would shoot down any UN planes that flew over his territory, said Mr Wek.

South Sudan has seen widespread violence between rebels and the national army since December.

Online Editors