South Sudan rebel leader Riek Machar agreed to send envoys to peace negotiations in Ethiopia Tuesday, but rejected face-to-face talks with President Salva Kiir, warning that his forces will continue to fight.
Machar, a former vice president accused of sparking deadly conflict by attempting a coup over two weeks ago, said his troops were still marching on the capital after claiming to have recaptured a key town.
"Our forces are still marching on Juba, there is no cessation of hostilities yet," Machar told AFP via satellite telephone from an undisclosed location inside South Sudan.
Ignoring a deadline from regional powers for an immediate ceasefire, he said any halt in the more than two weeks of fighting "needed to be negotiated".
"That is what the delegation is going to Addis Ababa to discuss and to negotiate," he said, adding the chance of him meeting with Kiir in person "depends on how the negotiations go".
The United States, which was a key backer of South Sudan's independence struggle, said the sending of negotiators was an "important first step", special envoy Donald Booth said.
Officials in the Ethiopian capital confirmed that delegations from both sides were due to land in Addis Ababa, the headquarters of the African Union, later Tuesday with talks expected to start on Wednesday.
"I will follow later, once the negotiations have resulted in a cessation of hostilities. It depends on if and when that is achieved," Machar said.
"We did not ask for this battle, it was forced upon us," Machar added, reiterating his position that it was the president who started the fighting on December 15.
South Sudan is the world's youngest nation, having only won independence from Khartoum in 2011, but has been beset by poverty, corruption and ethnic tensions, including between the president's Dinka tribe -- the largest in the country -- and Machar's Nuer community.
Thousands of people are feared to have been killed in over two weeks of fighting, pitching army units loyal to Kiir against a loose alliance of ethnic militia forces and mutinous army commanders nominally headed by Machar.
The AU expressed "Africa's dismay and disappointment that the continent's newest nation should descend so quickly into civil strife", warning of its potential to deteriorate into "full-fledged civil war" -- even though many observers say this has already happened.
Heavy fighting continued to rage on Tuesday, with the rebels claiming they had recaptured Bor, capital of the powder-keg Jonglei state and situated just 200 kilometres (125 miles) north of the capital Juba -- the third time the town has changed hands in two weeks.
"Bor is under our control... we are now in Bor town," rebel spokesman Moses Ruai told AFP.
South Sudanese army spokesman Philip Aguer disputed the claim, saying the fighting was ongoing inside the town. A UN spokesman had also confirmed the town was under attack earlier Tuesday.
'Full-fledged civil war'
Thousands have fled in recent days from Bor in fear of a counter-attack by rebels -- including an ethnic militia force dubbed the "White Army".
Across the country, the United Nations has estimated close to 200,000 people have been forced to flee their homes, of which 75,000 have sought protection from badly overstretched UN peacekeepers.
Fierce battles have been reported in strategic oil-producing areas -- with rebels controlling Bentiu, state capital of the key state of Unity, as well parts of the oil-rich Upper Nile State.
Industry sources say South Sudan's oil production has dropped by around a fifth because of the fighting.
There have also been grim reports of massacres, rapes and killings, prompting the African Union to threaten "targeted sanctions" over the conflict.
East Africa's regional IGAD bloc headed by Ethiopia -- which had set Tuesday as the deadline for talks to start -- said that negotiations "will focus on a monitored ceasefire" before more talks to settle "underlying political problems."
Kiir has described the war as "senseless", but ruled out power sharing with the rebels.
"What power sharing? It is not an option.
This man has rebelled.
If you want power, you don't rebel so that you are awarded with the power," Kiir said in an interview broadcast on the BBC Tuesday.
A key rebel demand has been the release of several top level political leaders arrested hours after the fighting began, but Kiir said they must follow the court process.
Ugandan President Yoweri Museveni has also warned that Machar must comply with the ceasefire deal or face action by regional nations.
He said if Machar does not respond "we shall have to go for him," without clarifying if his threat involved military action.