The government of South Sudan said on its Twitter feed on Friday that it "agreed in principle to a ceasefire to begin immediately, but our forces are prepared to defend themselves if attacked."

It came after a meeting of East African leaders in Nairobi on Friday, who urged South Sudanese President Salva Kiir and former Vice President Riek Machar to meet face-to-face and try to resolve their differences.

It follows the deaths of at least 1,000 people in December, during a wave of violence between the rival forces loyal to Kiir and his deposed former deputy, Machar. Kiir had accused Machar of attempting a coup against his government. There have also been concerns the conflict has moved away from being primarily political and has taken on ethnic dimensions, with the two men hailing from rival tribes.

The UN has sent peacekeepers and agreed earlier in the week to roughly double the number of troops present as the fighting continued. Similarly, EU foreign policy chief Catherine Ashton sent special representative Alex Rondos to South Sudan this week, to seek a political solution to the conflict.

The regional African leaders on Friday said they "welcomed the commitment by the Government of the Republic of South Sudan to an immediate cessation of hostilities," and told Machar to "make similar commitments."

In attendance were the heads of state of Kenya, Uganda, Ethiopia, Somalia and Djibouti, who met with South Sudan's vice president and the foreign minister. Neither Kiir nor Machar, who is in hiding, took part in the talks.

The leaders urged the pair to meet before the end of 2013, just days away, and added they would not accept the toppling of South Sudan's government by military force.

"If hostilities do not cease within four days, the summit will consider further measures," Ethiopian Foreign Minister Tedros Adhanom [seen above, speaking] told reporters. The talks came a day after three-way negotiations between Kiir, Kenyan President Uhuru Kenyatta, and Ethiopian Prime Minister Hailemariam Desalegn.

The fighting in South Sudan erupted in the capital Juba on December 15 and spread to a number of states. On Thursday, the UN mission in South Sudan said 50,000 civilians were seeking protection at its bases across the country, amid the many thousands more who had been forced to flee their homes.

Both sides remain locked in fierce battles for control of several strategic oil-rich areas in South Sudan's north. There have been heavy clashes in Malakal, the capital of the state of Upper Nile, where both government forces allied to Kiir and Machar's rebels have insisted they were in control.

South Sudan, the world's youngest country, gained independence from Sudan two-and-a-half years ago as part of a UN-sponsored peace deal, seeking to end a 22-year Sudanese civil war that claimed an estimated 2 million lives.

Release of coup-linked politicians

The push for talks may have received a glimmer of hope, with the reported release of two politicians out of a group of 11 arrested by the government, accused of plotting the alleged coup against Kiir. The release of the 11 prominent politicians is a key rebel condition for peace talks.

The news agency Reuters reported on Friday that presidential spokesman Ateny Wek Ateny said two of these politicians had been freed, and that another six would soon be released, but said three of the group would remain in custody over corruption allegations. Those politicians are former Finance Minister Kosti Manibe, ex-Cabinet Affairs Minister Deng Alor, and Pagan Amun, the former secretary general of the ruling Sudan People's Liberation Movement.

"We are following the legal avenue," Ateny told the news agency Reuters.

Earlier on Friday, the US envoy to South Sudan described the releases as a promising sign.

"We were very encouraged to hear the president reiterate that with the exception of three of the senior Sudan People's Liberation Movement [party] officials who have been detained...the others will be released very shortly," US Envoy Donald Booth told South Sudan state television.

Desperate humanitarian situation

The UN has estimated aid agencies need at least $166 million (121 million euros) for relief effrts in South Sudan. It says extra troops and "critical assets" such as helicopters would be on the ground by Saturday.

"We have heard reports of extra-judicial killings, arbitrary detentions of civilians, ill-treatment, abuse and also mass graves," Hilde Johnson, head of the UN mission in South Sudan told the news agency AP. "Our human rights officers have been working around the clock, throughout this crisis, and they are investigating these reports and allegations."

Johnson said UN troops were "overstretched" and needed extra manpower to be deployed with "unprecedented speed."

jr/msh (Reuters, AFP, dpa)