The United Nations says it is concerned by reports that thousands of armed youth loyal to former Vice President Riek Machar are preparing an attack on a South Sudan town.
A spokesman for the U.N. mission in South Sudan says a U.N. reconnaissance mission spotted a group of armed youths about 50 kilometers northeast of the central town of Bor. He says however that U.N. officials could not confirm how many people were in the group.
South Sudan's government claims that some 25,000 armed fighters from the Machar-backed force - the so called "White Army" - planned to attack the town, which was retaken by government forces this past week. The youth, like Machar, are ethnic Nuers while President Salva Kiir and his loyalists are ethnic Dinka.
Claims of the mobilization come as regional leaders attempt to broker a ceasefire.
The tribal violence erupted earlier this month, when the president accused Machar of attempting a coup.
The United Nations says the fighting has left more than 1,000 people dead and displaced tens of thousands.
A grouping of East Africa leaders announced Friday that South Sudan had agreed to a "cessation of hostilities" and the start of peace talks. The government also agreed to release eight of 11 political prisoners suspected of plotting the coup.
But Saturday, Machar ally Rebecca Nyandeng told VOA that Machar forces will not agree to cease-fire terms until the government releases all 11 prisoners.
Machar on Saturday stopped short of accepting the government offer. He told British radio the "mechanisms for monitoring" any agreement must first be established.