South Sudan's government and rebels loyal to Riek Machar, the sacked vice president, had agreed to peace talks. Both groups said they would send representatives to meet in Ethiopia.

On Tuesday, US envoy Donald Booth told the Associated Press that the commitment of both sides was "a first but very important step to achieving a cessation of hostilities" and the beginning of negotiations to resolve the crisis.

"The talks will focus on a monitored ceasefire followed by further dialogue aimed at solving the underlying political problems that led to the emergence of the present confrontation," a statement released by the Kenyan government, quoting an envoy for the Intergovernmental Authority on Development (IGAD), added.

IGAD member country Uganda had previously threatened to send troops to defeat Manchar's forces if the Tuesday ceasefire deadline was not met.

Violence has spread through the oil-producing country since December 15, when South Sudan President Salva Kiir accused Machar of trying to overthrow him in a coup. The political battle evolved along ethnic lines with tensions raised between Kiir's Dinka and Machar's Nuer clan.

At least 1,000 people have been killed and more than 180,000 displaced as a result of the fighting in the world's newest nation.

Fighting continues despite peace step

Despite the political breakthrough, fighting continued on Tuesday with reports of rebels taking control of large parts of Bor, a strategic city which has become the site of a power struggle over the past fortnight, having been captured by rebels before being retaken by government troops a week ago.

Government troops battled forces loyal to Machar including the Nuer tribal militia called the "White Army" on Tuesday, military spokesman Philip Aguer said.

While rebel leader Riek Machar agreed to send representatives to the peace negotiations, he warned his forces would keep fighting.

"Our forces are still marching on Juba, there is no cessation of hostilities yet," Machar told news agency AFP via satellite telephone from an undisclosed location inside the country. Despite neighboring countries calling for the full laying down of arms, Machar said any halt to the fighting "needed to be negotiated."

"That is what the delegation is going to Addis Ababa to discuss," he added, saying whether he met Kiir in person would depend on the outcome of those negotiations.

The United Nations mission in South Sudan released a statement Tuesday saying it was "gravely concerned about mounting evidence of gross violations of international human rights law."

South Sudan gained independence from Sudan in 2011 following a civil war which killed more than two million people over 22 years.

se/kms (AP, AFP, dpa, Reuters)