A face-to-face meeting between South Sudan’s rival politicians is likely to take place on Friday in Ethiopia, UN chief Ban Ki-moon has said.
Both President Salva Kiir and his sacked former deputy Riek Machar had given him their assurances during his trip to South Sudan, he said.
A truce was agreed in January but fighting has continued.
More than a million people have fled their homes since the conflict erupted in December.
Fighting broke out after President Kiir accused Mr Machar of plotting a coup.
Mr Machar denied the charges, but then mobilised a rebel force to fight the government.
Over the last few days, South Sudan government troops have been trying to recapture the oil hub of Bentiu from rebels, but have been forced back amid heavy gunfire.
During his one-day visit to the capital, Juba, Mr Ban said the continuing conflict was “senseless”.
“What I have seen and heard today breaks my heart and enrages my soul,” the AFP news agency quoted Mr Ban as saying.
He said the country’s leaders “must support justice and accountability for the crime committed and they must act to address the root causes of the conflict”.
It was John Kerry, the US secretary of state, who got Mr Kiir and Mr Machar to commit to a meeting during his visit to South Sudan last week.
Mr Ban said the assurances he had received meant the talks in Addis Ababa could happen on Friday.
He added, however, that Mr Machar had told him that as he was currently in the bush, he may not be able to make it by Friday, but he would try his best.
The power struggle between the two men – who fought together in the civil war before South Sudan’s independence – has increasingly taken on an ethnic dimension.
Mr Kiir is a member of the country’s largest group, the Dinka, while Mr Machar is from the second-biggest, the Nuer.
Both sides have been implicated in atrocities and war crimes and thousands of people have taken refuge at the various UN bases across the country.
The UN has about 8,500 peacekeepers in South Sudan, which became the world’s newest state after seceding from Sudan in 2011.