UN Secretary General Ban Ki-moon has said that South Sudan's rebel chief has agreed to direct peace talks, hours after the UN leader arrived in South Sudan to demand an end to a brutal civil war.
Leaders on both sides have previously defied peace agreements despite bloodshed and famine.
Rebel chief Riek Machar has now agreed to the idea of peacetalks, AFP news agency has reported.
Tuesday's visit, which comes as rebels and government forces battle for control of a key oil town, is the latest major push for a ceasefire in the nearly five-month-old conflict that has seen the world's youngest nation collapse amid a brutal cycle of war crimes.
"The Secretary-General has repeatedly called on the leaders to find a political solution, and to put an immediate end to the violence which has led to the suffering of so many innocent civilians," a report by the AFP news agency quoted a UN statement as saying.
Both sides in the conflict have been accused of widespread ethnic massacres, rape and the recruitment of thousands of child soldiers.
Al Jazeera's Anna Cavell, reporting from Juba, said that Ban's first priority during his one-day visit, which includes a meeting with President Salva Kiir, was the protection of civilians living on UN bases.
With about 80,000 people taking shelter in UN bases across the country, including 20,000 in the capital, "people have considered this to be a great success for the UN as it fulfills its mandate to protect civilians," Cavell said.
"But now, what we have is a potential long-term problem for the UN as these bases are not sanitary, and a lot of them are not fit for humans to live in.
"Also, very recently in the town of Bor, we saw civilians sheltering in a base come under attack from the outside despite the presence of UN peacekeepers," Cavell said.
Many of the occupants are too frightened of attacks to leave the protection of the peacekeepers.
Warning of sanctions
Ban's arrival comes days after US Secretary of State John Kerry flew into the capital, a visit in which he extracted promises from Kiir to meet face-to-face with rebel chief Riek Machar, a former vice-president who leads the rebel forces.
But despite warnings of US sanctions if fighting continued, the government has pushed forward a major offensive to claw back towns from the rebels, capturing one of their strongholds and forcing Machar to flee into the bush.
Kerry, who had already threatened US sanctions on the warring parties, has since warned of "serious implications" unless the fighting stops.
Ban last visited South Sudan amid euphoric celebrations at its independence from Sudan in July 2011, after it voted to split away following decades of war with Khartoum.
But as he arrived on Tuesday, battles raged around the dusty northern town of Bentiu, capital of the oil-producing Unity state, four days after government troops moved to wrest back control.
The war has claimed thousands, and possibly tens of thousands, of lives, with at least 1.2 million people forced to flee their homes.