Displaced women, including foreigners, queue inside the United Nations camp where they have sought shelter in Malakal, South Sudan, Monday, Dec. 30, 2013. When violence broke out in Juba on Dec. 15 life remained calm but tense in Malakal, the capital of oil-producing Upper Nile state, but the violence then radiated outward from Juba and full-fledged war broke out in the town on Christmas Day, as army commanders defected and pledged allegiance to the country's ousted vice president, in most cases pitting the ethnic group of President Salva Kiir, a Dinka, against ethnic Nuers. A United Nations armored vehicle passes displaced people walking towards the U.N. camp where they have sought shelter in Malakal, South Sudan, Monday, Dec. 30, 2013. A United Nations camp that has become home to the displaced living in makeshift tents is seen from an airplane over Malakal, South Sudan Monday, Dec. 30, 2013. A river choked with vegetation snakes its way through the landscape, seen from an airplane over South Sudan, Monday, Dec. 30, 2013. A United Nations helicopter offloads supplies at the airport, to be taken to a nearby U.N. camp where the displaced have sought shelter, in Malakal, South Sudan Monday, Dec. 30, 2013. JUBA, South Sudan (AP) - Uganda's president on Monday warned South Sudan's rebel leader against rejecting the government's offer of a cease-fire, saying regional leaders would unite to "defeat" the former vice president who is accused of mounting a failed coup in the world's newest country. Ugandan President Yoweri Museveni told reporters in Juba, the South Sudan capital, that a regional bloc known as IGAD had given Riek Machar "four days to respond" to the cease-fire offer. "If he doesn't we shall have to go for him, all of us," he said, referring to IGAD. A meeting of East African leaders last week said it "welcomed the commitment" by South Sudan's government to cease hostilities against rebels and urged both sides to start peace talks by Tuesday. Machar instead called for a negotiated cease-fire that includes a way to monitor compliance. Violence since mid-December in South Sudan has displaced up to 180,000 people, the United Nations said Monday. Uganda's influence is strong in South Sudan, where special forces from the neighboring country have been deployed at the request of South Sudan's President Salva Kiir, raising questions about the impartiality of Uganda as a possible mediator in a conflict that many fear could lead to civil war in the world's newest country. Museveni and Kiir are strong allies. The Ugandan leader is believed to be concerned about the security implications for Uganda of a violent takeover of South Sudan's government. For years the brutal warlord Joseph Kony, who once operated in the expansive jungle that now falls within South Sudan's territory, was a source of tension between Uganda and Sudan. Sudan's government faced persistent allegations of supporting Kony's rebellion against Uganda's government. Kony was forced to flee, and is thought to have fled to Congo and then Central African Republic, as the south moved closer to independence from Sudan. South Sudan peacefully broke away from Sudan in 2011 after a decades-long fight for independence, giving Uganda a new sense of border security. Uganda, one of the South's strongest supporters in its quest for independence, denies it has taken sides in South Sudan's latest conflict, saying its forces provided security as Western countries and others safely evacuated their citizens from South Sudan. Ugandan military spokesman Lt. Col. Paddy Ankunda insisted Monday that Ugandan forces are stationed only at the international airport in Juba and that their task is to "facilitate evacuation of civilians." But United Nations workers in Juba told The Associated Press that Ugandan troops have been guarding the only bridge that crosses the Nile River. Although Juba is now calm, unrest persists in other parts of the country. Col. Philip Aguer, the South Sudanese military spokesman, said Monday that, although there was "no major fighting" over the weekend, tension remained because "Machar has not committed himself to a cease-fire. We've not seen one. Pro-Machar forces still control Bentiu, the capital of oil-producing Unity state, and renegade troops are poised to attack Bor, the contested capital of Jonglei state, according to Aguer. "There's a force advancing toward Bor," he said. Although Kiir insists the latest unrest was sparked by a coup mounted by soldiers loyal to Machar late Dec. 15, this account has been disputed by some officials with the ruling party who say violence broke out when presidential guards from Kiir's majority Dinka tribe tried to disarm guards from the Nuer ethnic group of Machar. South Sudan has been plagued by ethnic tension and a power struggle within the ruling party that appears to have escalated after Kiir sacked Machar as his deputy earlier this year. Machar has criticized Kiir as a dictator and says he will contest the 2015 presidential election. The U.N., South Sudan's government and other analysts say the dispute is political at its heart, but has since taken on ethnic overtones. The fighting has killed more than 1,000 people, according to the U.N. Associated Press reporter Elias Meseret in Addis Ababa, Ethiopia, contributed to this report.