Leaders from the East African bloc, the Intergovernmental Authority on Development (IGAD), gathered in the Ethiopian capital to "deliberate on the current situation in the Republic of South Sudan", a statement read.
South Sudanese media said President Salva Kiir is due to attend, but no direct talks between Kiir's government and the rebels were due to take place until next week.
Ministers met late yesterday ahead of the main summit, including officials from Djibouti, Ethiopia, Kenya, Somalia, Sudan, South Sudan and Uganda.
South Sudan's government has been at war with rebel groups since December 15, when a clash between troops loyal to Kiir and those loyal to sacked vice president Riek Machar snowballed into full-scale fighting across the world's newest nation.
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Somalia's Prime Minister Abdiweli Sheikh Ahmed, who said he is to attend the meeting, said that "the IGAD summit is intended to tackle means of implementing previous agreements and the deployment of peacekeeping forces to South Sudan."
The two sides signed an IGAD-brokered ceasefire agreement on January 23, but heavy fighting has continued.
Ethiopian Prime Minister Hailemariam Desalegn this week said the peace process was "going very slow, but it is going in the right direction."
Over 930,000 civilians have fled their homes since fighting began, including over quarter of million leaving for neighbouring nations as refugees, according to the United Nations.
The meeting comes a day after the African Union opened a special commission of enquiry into atrocities, which at times has included brutal ethnic tit-for-tat killings.
Former Nigerian president Olusegun Obasanjo, who was sworn in as head of the five-member AU commission, vowed that "whoever is responsible must not get away with impunity."