South Sudan rebels have seized a key town as days of fierce fighting sparked fears of a descent into civil war, with regional countries scrambling to kick-start peace efforts.
Rebelling troops loyal to fugitive former vice president Riek Machar seized the town of Bor late on Wednesday, army spokesman Philip Aguer said, as fighting continued following an alleged failed coup bid against South Sudan President Salva Kiir.
"Our soldiers have lost control of Bor to the force of Riek Machar late on Wednesday ... there was shooting last night," Aguer told AFP.
He confirmed that about 450 people had been killed in Juba since battles broke out late on Sunday, including around a hundred soldiers, but added that troops had "restored calm" in the capital of the world's youngest nation.
The United Nations peacekeeping mission said it was sheltering civilians in five state capitals, including Juba and Bor, as well as in Bentiu, the main town of the crucial petroleum-producing state of Unity.
Foreigners are being evacuated from the troubled country, with the United States and Britain sending in flights for their citizens, and others fleeing overland south to Uganda.
Long lines of aid workers and expatriates began crowding Juba's airport on Wednesday waiting to board the first flight they could out of the country.
Hundreds of people have been killed and thousands more terrified civilians have fled their homes to seek protection at UN bases since the fighting broke out.
UN leader Ban Ki-moon warned on Wednesday that the fighting could spread.
"There is a risk of this violence spreading to other states, and we have already seen some signs of this," he said, adding the crisis "urgently needs to be dealt with through political dialogue."
There were fears that the poor and unstable nation, which broke free from Sudan in 2011, could slide back into all-out conflict.
"The scenario many feared but dared not contemplate looks frighteningly possible: South Sudan, the world's newest state, is now arguably on the cusp of a civil war," the International Crisis Group (ICG) think tank warned Thursday.
Top ministers from four regional nations flew in on Thursday to try to kick-start peace efforts.
Kenya's Foreign Minister Amina Mohammed, who said she was "en route to South Sudan to offer first hand assistance", said she was working with diplomats from Djibouti, Ethiopia and Uganda.
"It's a regional issue and the government of Kenya must be part of the solution process," she said.
All are members of a regional body, the Inter-Governmental Authority on Development (IGAD), whose members played key roles in pushing forward the 2005 deal that ended Sudan's two-decades long civil war with the south.
President Kiir has blamed the bloodshed on an attempted coup bid by his arch-rival Machar, but has said he was ready to "sit down" with him to try to solve the crisis.
But Machar, who was sacked by the president in July and is now on the run, has denied any coup attempt, and in turn accuses Kiir of using it as an excuse to purge his political rivals.
Security forces have arrested 10 key figures after the fighting began, many of them former powerful ministers.
"Kiir wanted to use the alleged coup attempt in order to get rid of us," Machar told the Paris-based Sudan Tribune website.
The battles have also raised fears of ethnic conflict, with Kiir coming from the majority Dinka people and Machar from the Nuer.
However, the government has been swift to say the clashes are over power and politics, noting that both sides include leaders from different tribes.
