First S Sudan ceasefire talks in Ethiopia 'fruitful'
Juba's military hospital has more than 1,000 patients in its 130-bed facility
Initial meetings in Addis Ababa between mediators and the warring parties in South Sudan have been "fruitful," Ethiopia's foreign minister has said.
Tedros Adhanom said direct talks between the two sides, aimed at ending the violence, would begin on Saturday.
Fighting between supporters of President Salva Kiir and those of his sacked deputy Riek Machar has killed at least 1,000 people since 15 December.
The US has announced a further cut of its embassy staff in South Sudan.
More than 180,000 people have been displaced in the conflict. Aid workers say many are living without shelter, clean water and sanitation.
Tensions are increasing around the rebel-held cities of Bor, in Jonglei state, and Bentiu, in the northern state of Unity.
A build-up of military personnel around both cities has prompted fears that renewed heavy fighting may be imminent as the government attempts to regain control, the BBC's Alastair Leithead reports from the capital, Juba.
One rebel spokesman told Reuters its troops were marching towards Juba, while a spokesman for the government said its forces were closing in to recapture Bor.
Evacuation flightDelegates from both sides began arriving in the Ethiopian capital on Wednesday but talks were delayed until the full negotiating teams had arrived.
The BBC's Emmanuel Igunza in Addis Ababa says the rival teams are in the same hotel but are currently in talks only with mediators.
Grang Demebiar, left, part of the negotiating team backing Riek Machar, arrives for talks in Addis Ababa 
A government soldier patrols Malakal in Upper Nile State 
These refugees in the town of Awerial are among the 180,000 people estimated displaced by the conflict The mediators are preparing the ground for direct talks, he adds.
Observers have said the discussions are likely to be complicated, as the two sides will have to agree on a mechanism to monitor any ceasefire.
Toby Lanzer, UN mission in S Sudan: "Situation continues to be very, very volatile"
Meanwhile, the US state department said it had ordered a "further drawdown" of its embassy staff in Juba "because of the deteriorating security situation".
It evacuated a large number of non-essential staff soon after the fighting began on 15 December.
But ambassador Susan Page told Reuters: "We are not suspending our operations. We are just minimising our presence."
However, the state department also said that, from Saturday, it would no longer be providing consular services to US citizens in South Sudan.
And it repeated its advice to its citizens to leave the country, announcing a further evacuation flight from Juba "to the nearest safe haven country" on Friday.
The United Nations, however, is flying more staff into Juba to help in the aid effort and to protect civilians' human rights. One official said US staff working for the UN had not been asked to leave.
South Sudan is the world's newest state. It was formed in 2011, gaining independence from Sudan after decades of conflict.
The latest trouble has its roots in tensions that go back long before 2011, rebels were fighting each other as well as for independence.
But what began as a squabble between former fighters turned politicians has taken on an ethnic dimension.
Politicians' political bases are often ethnic. President Kiir is from the Dinka community while Mr Machar is a Nuer.
Mr Kiir has ruled out any power-sharing arrangement with his rival in the longer term.
Fighting erupted in the South Sudan capital, Juba, in mid-December. It followed a political power struggle between President Salva Kiir and his ex-deputy Riek Machar. The squabble has taken on an ethnic dimension as politicians' political bases are often ethnic. 
Sudan's arid north is mainly home to Arabic-speaking Muslims. But in South Sudan there is no dominant culture. The Dinkas and the Nuers are the largest of more than 200 ethnic groups, each with its own languages and traditional beliefs, alongside Christianity and Islam. 
Both Sudan and the South are reliant on oil revenue, which accounts for 98% of South Sudan's budget. They have fiercely disagreed over how to divide the oil wealth of the former united state - at one time production was shutdown for more than a year. Some 75% of the oil lies in the South but all the pipelines run north 
The two Sudans are very different geographically. The great divide is visible even from space, as this Nasa satellite image shows. The northern states are a blanket of desert, broken only by the fertile Nile corridor. South Sudan is covered by green swathes of grassland, swamps and tropical forest. 
After gaining independence in 2011, South Sudan is the world's newest country - and one of its poorest. Figures from 2010 show some 69% of households now have access to clean water - up from 48% in 2006. However, just 2% of households have water on the premises. 
Just 29% of children attend primary school in South Sudan - however this is also an improvement on the 16% recorded in 2006. About 32% of primary-age boys attend, while just 25% of girls do. Overall, 64% of children who begin primary school reach the last grade. 
Almost 28% of children under the age of five in South Sudan are moderately or severely underweight - this compares with the 33% recorded in 2006. Unity state has the highest proportion of children suffering malnourishment (46%), while Central Equatoria has the lowest (17%). 
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