Mediators pressed for a ceasefire in South Sudan as government troops fought for control over the last rebel-held town.
Envoys from the United States and South Sudan's neighbours met on Saturday with Riek Machar, the former vice president who heads the rebel forces that have been fighting government troops for the past month, the rebels said.
"The American Special envoy to South Sudan and Sudan, Donald Booth together with [regional] mediators travelled to an undisclosed location in South Sudan to meet Dr Riek Machar," said a statement signed by Machar's former press officer Miyong G Kuon.
There were unconfirmed news reports that mediators would meet President Salva Kiir on Monday.
The meeting with Machar comes as talks in the Ethiopian capital Addis Ababa appear to be stalling. Mediators for the East African regional bloc IGAD have been trying to incorporate the proposals of both sides into a draft ceasefire document.
Fighting erupted in South Sudan on December 15. Kiir accused Machar of attempting a coup, while Machar in turn accused Kiir of using the coup accusation as an excuse to carry out a purge.
The biggest stumbling block in peace talks is still the 11 Machar sympathisers arrested by Kiir's forces shortly after the fighting began.
Machar's side has insisted the detainees should be released so they can take part in the talks, while Kiir is equally adamant they should face justice.
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UN chief Ban Ki-moon and the Security Council have both urged Kiir to free the 11 in order to kickstart the stalled talks.
On the ground in South Sudan, the full extent of the destruction wrought during recent battles began to emerge on Sunday.
An AFP photographer touring villages around Bentiu, the Unity state capital, which government forces wrested back from rebels on Friday, saw corpses lying in the streets and the thatched roofs of torched mud huts still smouldering.
Meanwhile, the Satellite Sentinel Project, co-founded by Hollywood star George Clooney, released images detailing destruction to homes and markets in two towns, Mayom in oil-rich Unity and Bor, the Jonglei state capital, which government forces are trying to take back from rebels for the second time in a month.
"Evidence of atrocities against civilians should be collected and used for future prosecution for war crimes. There will be no peace if massive human-rights abuses can be committed with no accountability," Clooney said in a statement. "This time in South Sudan there needs to be an end to impunity."
Fighting continued around the flashpoint town of Bor, rebel military spokesman General Lul Ruai Koang told the AFP news agency.
"We are still holding our positions, but the government forces are shelling them," he said, adding he did not know whether close combat was also taking place.
The fighting has forced nearly 400,000 people to flee their homes and caused "very substantially in excess" of 1,000 dead, according to the United Nations.
Of those forced to flee, about 350,000 are internally displaced and the remainder have fled to neighbouring countries.