JUBA: The United States and other foreign powers stepped up pressure on South Sudan's feuding ethnic factions to settle their differences, as Washington dispatched an envoy to the violence-wracked region.

US Secretary of State John Kerry said Friday he was sending a special envoy to encourage talks between opposing factions in the world's newest country, which has erupted into brutal fighting with a mounting death toll.

“Now is the time for South Sudan's leaders to rein in armed groups under their control, immediately cease attacks on civilians, and end the chain of retributive violence between different ethnic and political groups,” Kerry said, as he announced plans to dispatch Ambassador Donald Booth, his special envoy for Sudan and South Sudan, to the region.

The announcement came one day after President Barack Obama said in a message to Congress that the United States has deployed 45 troops to protect US personnel and assets in South Sudan.

African ministers also were stepping up pressure on President Salva Kiir to start talks with his former vice president Riek Machar, and met with the president Friday in the capital, Juba.

United Nations Secretary General Ban Ki-moon denounced the violence for the second time in as many days, issuing an appeal Friday for renewed efforts to restore peace.

He called for “all parties to exercise restraint, and to cease hostilities”, one day after an attack on a UN base killed at least 11 civilians and two Indian peacekeepers.

Violence erupted after a meeting last week of leaders of the ruling Sudan People's Liberation Movement (SPLM) failed to ease tensions in the party.

Kiir has accused Machar, whom he fired in July along with his entire cabinet, of staging an attempted coup. The former vice president has denied the charge, but his whereabouts are unknown.

Even as diplomatic initiatives were multiplying in South Sudan, the death toll continued to climb as violence spread between rival ethnic groups.

Six days into the battles between followers of Kiir, an ethnic Dinka, and Machar, a Nuer, at least 500 people have been killed in Juba alone.

Foreign governments meanwhile scrambled to get their nationals out of harm's way.

Obama said Thursday that the contingent of US troops sent this week “will remain in South Sudan until the security situation becomes such that it is no longer needed”.

“Although equipped for combat, this force was deployed for the purpose of protecting US citizens and property,” he added.

Obama has warned that hopes for South Sudan at its independence from Sudan in July 2011 are now “at risk”.

Britain sent a second military transporter to Juba on Friday to evacuate 93 people from the country.

China National Petroleum Corporation started pulling its workers out of South Sudan's oil fields and other Chinese firms followed the move, China's foreign ministry said.

Uganda said it also deployed special forces to get its nationals out of Juba and help secure the city.

Scramble to escape.

The ethnic divide grew with reports from around the country of killings of Dinka and Nuer.

UN officials reported that up to 3,000 armed youths had gathered around a camp where 14,000 people have sought refuge at Bor, the main town in Jonglei state.

France's UN envoy Gerard Araud said after emergency UN Security Council talks Friday that there was “heavy fighting” in Bor and worries about where the youths might be heading.

Troops loyal to Machar seized Bor on Wednesday.

The UN says more than 35,000 people are sheltering in its compounds across the country, and Juba airport was packed with foreigners scrambling to escape the chaos.

UN chief Ban on Friday urged leaders of the ruling SPLM “to resolve their personal differences through dialogue immediately”.

Earlier on Friday, Edmond Mulet, assistant UN secretary general for peacekeeping, briefed the closed Security Council meeting on still more clashes, diplomats said.

Nuer youth entered one oil facility at Bentiu in Unity state and ordered all ethnic Dinka employees to step forward and then killed them, Mulet quoted witnesses as saying.

At least five employees were killed, according to UN sources in South Sudan.

Mulet, who said there had been at least 500 deaths in Juba since the fighting started on Sunday, said Kiir had agreed to “unconditional dialogue” with his opponent to end the crisis.

The UN was still verifying the toll in the rest of South Sudan.

He said there were more than 35,000 people in UN bases around the country, including 20,000 at two compounds in Juba and 14,000 at another in Pibor in Jonglei state.

The UN mission is also sheltering civilians in Bentiu, the main town in Unity state.

South Sudan gained independence from Sudan as part of a peace process after a two-decade civil war that left two million dead.

But it has never been able to heal its own ethnic rivalry.