East African leaders have called on South Sudanese President Salva Kiir and political rival Riek Machar to meet face-to-face within four days to end the escalating violence in the world's youngest nation.
The leaders added that they would not accept South Sudan's government being toppled through use of military force.
"If hostilities do not cease within four days, the summit will consider further measures," Ethiopian Foreign Affairs Minister Tedros Adhanom told journalists at the end of the meeting in Nairobi.
Kiir met with Kenyan President Uhuru Kenyatta on Thursday in the capital Juba.
But Machar sent a defiant message via BBC on Friday declaring that the conditions for a ceasefire had not been met. He noted that only two of his allied politicians have been released from detention of the 11 he wants freed.
The detainees are charged with attempting a coup to overthrow Kiir.
Fighting that erupted on December 15 in Juba and spread rapidly reportedly claimed hundreds of lives and displaced tens of thousands of people.
Heads of state from Kenya, Uganda, Ethiopia, Somalia and Djibouti met with South Sudan's foreign minister and Sudan's vice-president.
Machar, who is in hiding, has accused the president of being dictatorial, while Kiir has expressed a willingness to negotiate an end to the fighting and to enter talks unconditionally.
"There should be immediate cessation of violence," Kenyatta said during the closed session, according to a tweet by his spokesman Manoah Esipisu.
"South Sudan's government must guarantee security of all its citizens."
The leaders were meeting as part of an extraordinary summit of the Intergovernmental Authority on Development (IGAD), a day after three-way talks in South Sudan's capital Juba between Kiir, Kenyatta and Ethiopian Prime Minister Hailemariam Desalegn.
Ethiopia said the Juba meeting had been constructive.
The conflict has taken on ethnic dimensions. Kiir belongs to the Dinka, the largest group in South Sudan, and Machar is from the Nuer people.
There have been growing tensions in the ruling Sudan People's Liberation Movement since independence.
An intensifying power struggle between Kiir, who has a military background with little formal education, and Machar, who has a doctorate from Britain, peaked when key politicians challenged Kiir's candidacy for the 2015 elections.
That Kiir and Machar come from different ethnic groups and regions within South Sudan caused further political ruptures.
The violence has been particularly intense in Central Equatoria, Jonglei and Unity states, according to the United Nations Office for the Coordination of Humanitarian Affairs.
At least 120,00 people had been displaced in the conflict, the United Nations said on Friday, while some 63,000 people have sought shelter at UN peacekeeping bases throughout the country.
The UN also cautioned that the real number of refugees was likely to be much higher, as it was difficult to reach people in areas where fighting was continuing.
Neighbouring Uganda has received more than 7000 South Sudanese refugees since last week, the Red Cross said.
