South Sudanese rebels and government negotiators are set to begin their first face-to-face talks, in an effort to thrash out a ceasefire deal to end weeks of fighting in the country.

The talks were set to start on Sunday after several days of delay, and have been overshadowed by continued clashes between President Salva Kiir's SPLA government forces and rebels loyal to former Vice President Riek Machar.

"We envisage a rapid agreement of the cessation of hostilities and ceasefire arrangements in order to create a conducive atmosphere for addressing outstanding political issues," government representative Niag Deng Nial said at a ceremonial opening to the talks at a luxury hotel in the Ethiopian capital of Addis Ababa on Saturday.

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"Our people have suffered a lot during the struggle for our independence and they should not suffer again in our hands," he added.

The talks will focus on when and how to roll out the ceasefire that both sides have agreed to in principle, though neither has indicated a start date.

The head of the rebel delegation, Taban Deng Gai, has repeated Machar's call for the release of several senior politicians allied to the former vice president and for the state of emergency imposed by Kiir in two regions of South Sudan to be lifted.

"With the current mass killing going on in the country and political detention, there can be no conducive atmosphere for peace talks," he said.

Fears of civil war

Western and regional powers, many of which supported the negotiations that led to South Sudan's independence from Sudan in 2011, are pressing for a peace deal, fearing the new fighting could slide into civil war and destabilise east Africa.

US Secretary of State John Kerry voiced support for direct South Sudanese peace talks set to begin on Sunday and cautioned against any use of force to try to gain the upper hand.

"Both parties need to put the interest of South Sudan above their own," Kerry told reporters in Jerusalem.

Peace talks had been delayed for days because the two sides were unable to agree upon an agenda, officials said. The slow start is a worrying sign for South Sudan, which has been embroiled in violence for weeks, with Kiir accusing Machar of an attempted coup.

Clashes have already killed more than 1,000 people, driven 200,000 from their homes and rattled oil markets.

Forces loyal to Machar now control two state capitals, including the strategically located town of Bor.

On Saturday, the South Sudanese army battled to wrest back control of Bor, with reports of intense battles involving tanks and artillery.

Source: Agencies