Key South Sudan city taken over by renegade militia

South Sudan's central government lost control of the capital of a key oil-producing state on Sunday, the military said, as renegade forces loyal to a former deputy president seized more territory in fighting that has raised fears of full-blown civil war in the world's newest country.

Bentiu, the capital of oil-rich Unity state, is now controlled by a military commander loyal to former Vice-President Riek Machar, said Col. Philip Aguer, the South Sudanese military spokesman.

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

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The armed rebels were said to be in control days earlier of some of South Sudan's oil fields, which have historically been a target for rebel movements, endangering the country's economic lifeblood.

South Sudan gets nearly 99 per cent of its government budget from oil revenues, and the country reportedly earned $1.3 billion in oil sales in just five months this year, according to the London-based watchdog group Global Witness.

Although the country's capital, Juba, is mostly peaceful a week after a dispute among members of the presidential guard triggered violent clashes between military factions, fighting continues as the central government tries to assert authority in the states of Unity and Jonglei.

Bor, the capital of Jonglei, is said to be the scene of some of the fiercest clashes between government troops and rebels.

Michael Makuei Lueth, South Sudan's information minister, said Machar was believed to be hiding somewhere in Unity state.

"He is a rebel, he's a renegade and we are looking for him. He's moving in the bushes of South Sudan,"Luethsaid ofMachar.

UN 'not abandoning' region

The UNMission in South Sudan said in a statement Sunday that all non-critical staff members inJubaare being evacuated to Uganda. The mission said the move was "a precautionary measure to reduce pressures on its limited resources" as it continues to provide assistance and shelter to more than 20,000 civilians gathered inside its compounds inJuba, the mission said in a statement.

To anyone who wants to threaten us, attack us or put obstacles in our way, our message remains loud and clear: we will not be intimidated.-HildeJohnson, the UNsecretary-general's envoy in South Sudan

HildeJohnson, the UNsecretary-general's envoy in South Sudan, said the evacuation doesn't mean the UNis "abandoning" South Sudan.

"We are here to stay, and will carry on in our collective resolve to work with and for the people of South Sudan," she said. "To anyone who wants to threaten us, attack us or put obstacles in our way, our message remains loud and clear: we will not be intimidated."

Hundreds have been killed in the fighting and world leaders are concerned about civil war in a country with a history of ethnic violence and divided military loyalties.

The U.S. and other countries have been evacuating their citizens from South Sudan. The U.S. has evacuated about 680 Americans and other foreign nationals so far, State Department spokeswomanJenPsakisaid in a statement.

President Barack Obama told U.S. Congress he may take further military action to protect Americans in South Sudan. In a letter to Congress, Obama said that about 46 U.S. troops were deployed Saturday to help evacuate Americans. That's in addition to another 45 troops deployed to reinforce the U.S. Embassy in Juba.

Obama is on his annual vacation in Hawaii, but he said in the letter to congressional leaders that he's monitoring the situation.

"I may take further action to support the security of U.S. citizens, personnel, and property, including our Embassy, in South Sudan," Obama wrote.

Dinka vs Nuer

On Saturday, gunfire hit three U.S. military aircraft trying to evacuate American citizens inBor, wounding four U.S. service members in the same region gunfire downed a UNhelicopter on Friday. It remains unclear how many U.S. citizens are still stranded inBorand other rural towns.

Earlier this week, the top military general inBordefected with his troops, starting a rebellion that appears to be spreading to other parts of the country.

AguersaidBoris still under the control ofpro-Macharforces, disputing reports the rebels had fled as government troops advanced onBor.

South Sudan's PresidentSalvaKiir, an ethnicDinka, said on Monday that an attempted military coup had triggered the violence, and the blame was placed onMachar, an ethnicNuer. But officials have since said a fight betweenDinkaandNuermembers of the presidential guard triggered the fighting that later spread across the East African country.

Machar'souster from the country's No. 2 political position earlier this year had stoked ethnic tensions.Machar, who has criticizedKiiras a dictator, later said he would contest presidential elections in 2015.

UNSecretary-General BanKi-moonon Sunday urged South Sudan's leaders "to do everything in their power" to stop the violence.

Foreign ministers fromneighboringcountries Kenya, Ethiopia, Uganda and Djibouti were in South Sudan earlier in the week to try and diffuse the crisis.

South Sudan, which became independent in 2011 after decades of a brutal war with Sudan, has been plagued by ethnic discord, corruption and conflict with Sudan over oil revenues.

Although the south inherited three-quarters of Sudan's oil production when it declared independence in 2012, its oil exports are pumped through pipelines running north, raising concern a rebel takeover of southern oil fields could invite Sudan into the conflict.