South Sudan has postponed presidential elections due next year to give government and rebel forces more time to achieve reconciliation, President Salva Kiir has said.
Mr Kiir and rebel leader Riek Machar signed a ceasefire deal on Friday to end conflict that erupted in December,
He said an interim government would run South Sudan until elections are held in 2017 or 2018.
Thousands of people have been killed in the fighting.
Mr Machar accused the government of breaking a ceasefire and attacking the rebels on multiple fronts.
The UN has accused both sides of crimes against humanity, including mass killings and gang-rape.
South Sudan is the world's newest state, becoming independent in 2011 after seceding from Sudan.
Fighting broke out in December after Mr Kiir accused Mr Machar, his sacked deputy, of plotting a coup.
Mr Machar denied the allegation, but then marshalled a rebel army to call for the overthrow of the government.
Mr Kiir and Mr Machar signed a peace deal in Ethiopia on Friday. It was their first meeting since the conflict erupted.
At least 1.5 million people have been left homeless in the world's newest state
Many of them are living at UN camps
Both the government and the rebels accuse each other of launching attacks in Bentiu
Both sides have accused each other violating the truce - the second ceasefire agreement since fighting broke out.
On Monday, rebel spokesman Lul Ruai Koang said government troops had recaptured the oil hub of Bentiu, where an ethnic massacre took place last month, after "extensive shelling" of villages around the town.
Mr Kiir was "acting with impunity", he said, Reuters news agency reports.
Earlier Mr Machar told the BBC's HARDTalk programme that despite accusing the government of violating the ceasefire, he wanted further "dialogue" with his rival.
Military spokesman Philip Aguer said there had been no fighting in South Sudan on Monday.
The government had earlier accused rebel forces of flagrant violations of the ceasefire deal.
The battle between Mr Kiir and Mr Machar has assumed ethnic overtones, with Mr Machar relying heavily on fighters from his Nuer ethnic group and Mr Kiir from his Dinka community.
The UN says hundreds of non-Nuers were killed in Bentiu last month when rebel forces captured the town.
The UN has about 8,500 peacekeepers in South Sudan. However, they have struggled to contain the conflict.
At least 1.5 million have been displaced by the conflict.
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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