'Atmosphere of fear' in South Sudan

The UN mission in South Sudan has urged rival political leaders to agree a truce and open negotiations.

Clashes broke out between troops loyal to President Salva Kiir and others backing his former deputy a week ago.

Machar's statement on Sunday comes amid fighting which has raged in one of the of the world's youngest countries for more than a week, after President Salva Kiir accused Machar of attempting a coup.

Machar has denied the allegation and accused Kiir of carrying out a vicious purge of his rivals.

Machar said he wanted to be the next leader of the country - to run for president at the next election in 2015. He called on Kiir to step down.

He said his troops were now in control of Bentiu, the capital city of Unity state where a military government has been established. 

South Sudanese military spokesperson, Colonal Philip Aguer, confirmed late on Sunday that the capital city had been lost to a commander loyal to Machar.

"Bentiu is in the hands of a commander who has declared support for Machar,'' he said. "Bentiu is not in our hands."

The fighting has left hundreds dead and sent tens of thousands of people fleeing for protection in UN bases or to safer areas of the country, which only won independence from Sudan in 2011 but has been blighted by ethnic divisions, corruption and poverty.

Special envoys from the US and Nigeria flew into the capital Juba on Sunday, following on from a mission by foreign ministers from east Africa and after an appeal for an end to the violence from UN chief Ban Ki-moon.

Foreign governments, including those of the US, Britain, Uganda and Kenya, have been organising special evacuation flights to pull out their nationals. The US State Department said on Sunday it had safely evacuated American citizens and some other nationals from Bor by helicopter, in co-ordination with the UN and South Sudanese government.

On Saturday, four US servicemen were wounded when their planes were fired at in a rebel-held area.

At least one UN base has also come under attack in recent days - with the deaths of two Indian peacekeepers and possibly dozens of civilians.

President Barack Obama has warned against continued fighting.

"Any effort to seize power through the use of military force will result in the end of longstanding support from the United States and the international community," the White House said.

South Sudan's government, meanwhile, acknowledged that much of Unity State, the country's main oil-producing area, was in the hands of the rebels.

Machar denies government suggestions that rebels have been forced out of Bor, which is situated about 200km north of Juba, although South Sudan's army spokesman said government troops were advancing.

A local official in Bentiu said the area was littered with bodies following the fall of the town, which was prompted by the defection of a top government commander.

"There are so many bodies, over a hundred not yet buried," the local official, who asked not to be named, told AFP news agency.

Army spokesman Aguer said "Unity State is currently divided, with the SPLA and the loyalists to the government on one side and those who are supporting Riek Machar on the other."