UN Helicopter 'Shot Down' in South Sudan
The United Nations Mission in South Sudan said one of its helicopters crashed near the town of Bentiu. Reuters

The United Nations has said one of its helicopters has crashed in a restive region of South Sudan killing three crew members, amid reports it was shot down.

The UN mission in South Sudan (UNMISS) said the aircraft came down about 10km south of the town of Bentiu, in the northern Unity state.

A crew member survived the impact and was receiving treatment from the Médecins Sans Frontières (Doctors Without Borders) team in Bentiu, the mission said.

UNMISS tweeted:

The mission said the MI-8 helicopter was on a routine cargo flight from Wau in Western Bahr El Ghazal State to Bentiu, when it crashed.

The region has recently been the site of fierce fighting between the government and rebel forces.

UNMISS said it was launching an investigation to determine the cause of the crash.

Separately, a UN official speaking on condition of anonymity told The Associated Press that it appeared the helicopter was shot down.

"I wish to convey my heartfelt condolences to the families of the deceased and wish a full and speedy recovery to the injured crew member," said Toby Lanzer, the officer-in-charge of UNMISS.

South Sudan has been engulfed in a violent civil conflict that has caused the displacement of almost two million people in the last eight months.

Thousands have been killed since fighting erupted in December 2013, when a political power struggle broke out between President Kiir and his ex-deputy Riek Machar.