"We all recognize 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 on Monday would ward off any repercussions.
"They [government officials] have certain reservations" and have decided to go back home for consultations, Seyoum Mesfin said. "In the next 15 days, the president will come back to Addis Ababa and finalize the peace agreement."
Details of the deal between Amum and the rebels were not immediately known.
At least seven cease-fires 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 Monday ended 10 days of talks mediated by the regional eight-nation bloc the Intergovernmental Authority on Development, as well as the United Nations, the African Union, China, 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 country along ethnic lines.
Agence France-Presse
Error
Sorry, your comment was not saved due to a technical problem. Please try again later or using a different browser.