South Sudan peace talks to be concluded
However, the secretary-general of the ruling party and rebels signed an agreement committing them to peace.
Top party official Pagan Amum and rebel chief Riek Machar signed a deal, but mediators say Amum was not representing the government.
President Salva Kiir watched the signing, after briefly shaking hands with Machar.
"We all recognise this is a great day in the movement of the peace process in South Sudan," chief mediator Seyoum Mesfin said, but added that "the signing ceremony is not complete without the signing of the government."
The international community had threatened possible sanctions if a deal was not reached by the end of the day, but it was not clear if the result of talks today would ward off any repercussions.
"They (the government) have certain reservations and have decided to go back home for consultations. In the next 15 days, the president will come back to Addis Ababa and finalise the peace agreement," Seyoum Mesfin said.
Details of the deal between Amum and the rebels are not immediately known.
At least seven ceasefires have already been agreed and then shattered within days, if not hours in Africa's newest country, which broke away from Sudan in 2011.
Rival leaders have been under intense diplomatic pressure to end 20 months of a brutal civil war in which tens of thousands of people have been killed.
The ceremony today ended ten days of talks mediated by the regional eight-nation bloc IGAD, the Intergovernmental Authority on Development, as well as the United Nations, African Union, China and the "troika" of Britain, Norway and the United States.
South Sudan's civil war erupted in December 2013 when Kiir accused his former deputy Machar of planning a coup, setting off a cycle of retaliatory killings that has split the poverty-stricken, landlocked country along ethnic lines.
(File photo: Wikipedia)