The head of the UN peacekeeping mission in South Sudan has called for an end to fighting in the country, and for peace talks to be given a chance.
Hilde Johnson told the BBC the humanitarian situation was worsening.
At least 1,000 people have died since fighting erupted last month between supporters of President Salva Kiir and those of his sacked deputy Riek Machar.
Both sides have sent delegations to talks in Ethiopia but so far the rebels have not agreed to end hostilities.
Meanwhile, Mr Kiir has declared a state of emergency in two parts of the country affected by fighting and where rebels have taken control of large areas.
Heavy fighting is reportedly taking place in the key town of Bor.
People displaced by South Sudan fighting wait to cross the Nile in the town of Bor (December 30)
More than 120,000 people are believed to have fled their homes
The decree would allow officials in Jonglei and Unity states who had joined the rebels to be sacked without the need for a vote in the state parliament, the president’s spokesman said.
Among officials thought to have joined the rebels was the deputy governor of Jonglei.
What began as a power struggle between Mr Machar and President Kiir has taken on overtones of a tribal conflict. The Dinka, to which Mr Kiir belongs, are pitted against the Nuer, from which Mr Machar hails.
By sending a delegation to Addis Ababa, Riek Machar has agreed to one of the mediation’s key demands – but not the other. The rebel leader told me he would not order his troops to stop fighting. This is something, he said, that can be discussed in Ethiopia.
Regional leaders had wanted a cessation of hostilities and talks to begin by 31 December. The attack on Bor was a clear attempt by Mr Machar to show his military power, which will strengthen his hand in any negotiations.
It is interesting that Mr Machar is now admitting that the “white army” – an ethnic militia – is “part of” his army. This will not do much for his popularity in many parts of South Sudan.
“Violence has been committed by both sides. Unfortunately, elements on both sides have exploited the situation and have fuelled ethnic tension,” Ms Johnson told the BBC’s James Copnall in Juba.
She said the conflict had its roots in “a political struggle that needs a political solution” and called for “a major effort of national reconciliation” to address the historical reasons for current divisions.
Talks between the two sides in Ethiopia are due to begin on either Wednesday or Thursday.
Mr Kiir confirmed on Wednesday afternoon that a 14-member delegation had left for Ethiopia.
Observers say the discussions are likely to be complicated, as the two sides will have to agree on a mechanism to monitor a ceasefire.
Mr Kiir has already ruled out any power-sharing arrangement with Mr Machar in the longer term.
Mr Machar claimed his delegation would be headed by Rebecca Nyandeng, the widow of John Garang, who led South Sudanese rebel forces against Khartoum for many years – though she later denied this in a BBC interview.
As a Dinka, Ms Nyandeng would help Mr Machar challenge the allegation that his rebellion is primarily from his Nuer ethnic group.
Mr Machar’s forces are a mix of mutinous soldiers loyal to him and an ethnic militia called the “white army”, known for putting white ash onto their bodies as a kind of war-paint and insect repellent.
East African leaders have been leading mediation efforts to end the crisis.
President Yoweri Museveni from Uganda in Juba, 30 December
On Monday, Uganda’s President Yoweri Museveni threatened the rebels with military action if they failed to agree to a ceasefire by the end of Tuesday.
It appears that the pressure on Mr Machar worked, says the BBC’s James Copnall in the capital Juba, as the rebel leader appears to be sending a delegation despite Mr Kiir failing to agree to demands such as the release from jail of Mr Machar’s political allies.
But Mr Machar insists he will not order his troops to stop fighting before preliminary talks have taken place.
South Sudan is the world’s newest state. It was formed in 2011, gaining independence from Sudan after decades of conflict.