An army spokesman suggested the fighting could go on despite the announcement by politicians in a faraway capital.
At the meeting in Kenya, South Sudan agreed not to carry out a planned offensive to recapture Bentiu, the capital of oil-producing Unity state, which is controlled by troops loyal to Riek Machar, the former vice president vilified by the government as a corrupt coup plotter.
"We are not moving on Bentiu as long as the rebel forces abide by the cease-fire," said Michael Makuei Lueth, South Sudan's information minister.
But no one representing Machar was at the Nairobi meeting — a move possibly meant to deny him any elevated status that could also slow the search for peace. And Machar told the BBC that conditions for a truce were not yet in place.
In the field, the military reported no immediate changes in the battle for control of the world's newest country.
Said army spokesman Col. Philip Aguer: "We have not seen any sign of a cease-fire. There is no cease-fire agreed by the two sides," an indication the planned assault on Bentiu could still take place.
Elsewhere, the country's military advanced on the rebel-held town of Malakal early Friday and had taken control of it by noon, Aguer said.
Violence erupted Dec. 15 in South Sudan's capital Juba and quickly spread across the country. Ethnic Nuers — the group Machar is from — say they are being targeted by Dinkas, the ethnic group of President Salva Kiir.
The U.N., the South Sudan government and other analysts say the dispute is political at its heart, but has since taken on ethnic overtones.
The 25,000 people — mostly Nuers — sheltering at U.N. camps in Juba fear they would be targeted for death if they leave. Members of the government insist Juba's streets are safe for all.
The fighting has displaced more than 120,000 people and killed more than 1,000.
East African leaders meeting under a bloc called IGAD said in a statement Friday that they "welcomed the commitment" by the South Sudanese government to cease hostilities. The leaders also condemned "all unconstitutional action" to try to topple the government in Juba.
The joint statement urged Machar to make similar commitments to stop fighting. Indeed, the bloc laid bare how one-sided the talks have been so far as it directed its council of ministers to "make contact" with Machar.
The statement said face-to-face talks between the two sides should happen by Tuesday.
Speaking to the BBC by satellite phone, Machar said any cease-fire had to be negotiated by delegations from both sides and must include a way to monitor compliance.
In Juba's corridors of power, disdain for Machar is strong. Lueth said the former vice president is "on his way to hell if he's not careful" and that he could be executed by firing squad after a military trial.
South Sudan's government also says it will not release any of Machar's imprisoned compatriots, a condition Machar has set for his presence at the negotiating table.
Lueth said that no Machar representatives belonged at the table of power Friday in Nairobi.
"Is it a place for rebels? It would be a wrong approach to do it that way. This idea of trying to equate Machar with the government is not acceptable," he said.
Eric Reeves, a Sudan expert, said Machar may not have been party to any talks yet because he wants to enter any negotiations from a position of strength. Reeves said he's concerned Machar might try to make a deal with Sudan, which desperately needs the revenue it receives by moving South Sudan's oil to market.
One scenario Reeves outlined: Khartoum agrees to an arrangement in which Sudan's military, in the interests of regional security, protects Machar in his "stewardship" of the Unity oil fields.
Machar has already publicly floated the idea of sequestering oil revenue, Reeves said.
"This would be a desperate and vehemently condemned move by Khartoum," Reeves said. "But the most militaristic and anti-South elements are calling the shots in the regime. And the (Sudanese) economy continues to implode, without much in the way of international coverage."
Machar denies there was a coup attempt, and some officials with the ruling party insist violence broke out when presidential guards from Kiir's majority Dinka tribe tried to disarm guards from the Nuer ethnic group of Machar.
Machar has criticized Kiir as a dictator and says he will contest the 2015 presidential election. Kiir fired Machar as his deputy in July following a power struggle within the ruling party, stoking ethnic tensions in a country with a history of divided military loyalties.
In a speech at the Nairobi summit, Kenyan President Uhuru Kenyatta said there is "a very small window of opportunity to secure peace" in South Sudan.
After a decades-long fight for independence, South Sudan peacefully broke away from Sudan in 2011. It has been plagued by corruption, ethnic tension and a power struggle within the ruling party.
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Odula reported from Nairobi, Kenya.