Ugandan President Yoweri Museveni says East African nations have warned South Sudanese rebel leader Riek Machar to comply with a cease-fire or face action by regional nations.
Mr. Museveni, who met South Sudanese President Salva Kiir in South Sudan's capital Juba Monday, said Machar had been given four days to respond to the offer.
Regional leaders are pressing for face-to-face talks between Mr. Kiir and Machar, his deposed vice president, by December 31.
Uganda says it has troops stationed at Juba's international airport tasked with "facilitating evacuation of civilians," but United Nations workers in the city say the forces are more widely deployed. Mr. Museveni and Mr. Kiir are strong allies.
Meanwhile, Reuters reported that thousands of people have fled the flashpoint town of Bor, heeding government warnings that 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.
White Army youths are known for the white powder they use to cover their skin as an insect repellant. Like Machar, they are ethnic Nuers while President Kiir and his loyalists are ethnic Dinka.
CNN quoted Deputy Information Minister Rachel Nyedak Paul as saying she and other ethnic Nuer officials had spoken with White Army leaders on Monday and convinced them to retreat.
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.