JUBA - South Sudan's government said on Sunday rebels had seized the capital of a key oil-producing region and fears grew of all-out ethnic civil war in the world's newest country.
The UN announced it was trying to rush more peacekeeping forces to landlocked, impoverished South Sudan as foreign powers urged both sides to stop fighting, fearing for the stability of an already fragile region of Africa.
The South Sudan government said on its Twitter account it was no longer in control of Bentiu, the capital of Unity State.
"Bentiu is not currently in our hands. It is in the hands of a commander who has declared support for Machar," it said.
Information Minister Michael Makuei said on Saturday an army divisional commander in Unity State, John Koang, had defected and joined rebel leader and former Vice President Riek Machar, who had named him the governor of the state.
But the government in Juba said it was still in control of the oilfields crucial to the economy.
UN Secretary General Ban Ki-moon told a news conference in Manila the UN planned to send resources from other peacekeeping missions in the region to South Sudan.
"We are now actively trying to transfer our assets from other peacekeeping missions like MONUSCO (in the Democratic Republic of Congo) ... and some other areas," he said.
"And we are also seeking support from other key countries who can provide the necessary assets."
Clashes between rival groups of soldiers in the capital Juba a week ago have spread across the country, which won its independence from Sudan in 2011 after decades of war.
President Salva Kiir, from South Sudan's Dinka ethnic group, has accused Machar, a Nuer whom he dismissed in July, of trying to launch a coup. The two men have long been political rivals.
Machar dismissed the charge but has since said he is commanding troops fighting the government.