South Sudanese troops loyal to President Salva Kiir are shown at Bor airport after they retook it from rebels on December 25. Rebels and government troops are fighting in Bor, an official says East African nations have set a Tuesday deadline for two sides to engage in talks The rebels are loyal to South Sudan's former Vice President Riek Machar President Salva Kiir has said his forces "will fight" if Machar will not agree to talk (CNN) -- East African nations had set Tuesday as a deadline for the two sides fighting in South Sudan to talk. Instead, they fought heavily in the key town of Bor, undermining efforts to bring more than two weeks of violence to an end. Bor, the capital of oil-rich Jonglei state, was recaptured by the army last week in a bloody battle. But the latest clashes show that rebels loyal to former Vice President Riek Machar are unwilling to let go easily. South Sudanese Deputy Information Minister Rachel Nyedak Paul told CNN the deadline for a cease-fire expires Tuesday afternoon. Kiir told CNN's Arwa Damon in an interview Monday that African nations should have acted quickly to help quell the rebel forces. As soon as an attempted coup took place and violence broke out, "the original leaders and all African leaders should have come in with military support," so that the rebels would have been "crushed once and for all," he said. If the other side, led by Machar, does not agree to talk, then "we will fight," Kiir vowed. Sanctions threat If they don't, the leaders of the Intergovernmental Authority on Development warned they'll "take action" to stop the conflict that the United Nations says has killed more than 1,000 people and forced about 121,000 from their homes. Ugandan President Yoweri Museveni, at a news conference, said that if Machar does not agree to talks, the other countries will "go for him." Asked what that means, he said, "defeat him." The Peace and Security Council of the African Union, which met Monday in Gambia, called on all sides to "immediately and unconditionally cease hostilities" and engage in dialogue. The council urged Machar and others to commit to talks, as Kiir has done. It also warned it would take measures including "targeted sanctions" against those who incite violence and ethnic strife, hinder humanitarian efforts or harm civilians. White Army Bor, a strategically important town in the center of the country, has been a flashpoint for violence. Sudan People's Liberation Army spokesman Col. Phillip Aguer warned over the weekend that about 20,000 ethnic Nuer from the so-called White Army, an ethnic militia loyal to Machar, were headed to Bor. Paul, the deputy information minister, told CNN on Monday that government officials had persuaded the so-called White Army to retreat from the town. But members of the militia are involved in Tuesday's clashes, according to Paul -- suggesting that the agreement broke down. The youths are known as the White Army for the white powder they use to cover their skin as an insect repellent. Fighting first broke out on December 15 in the capital city of Juba. It then quickly spread across the country, with reports of mass killings that were lent credence by mass graves. No clean water, no food The violence has sparked a growing humanitarian crisis. At least 122,000 people have been displaced since the fighting began, according to the United Nations. About 63,000 of them have taken refuge in U.N. bases in the country. The nongovernmental organization Doctors Without Borders said Monday that aid is urgently needed for 70,000 people who have fled the fighting in Bor. They have sought shelter in the town of Awerial, in neighboring Lakes state, but the town is ill-equipped to cope with the influx, it said. "Living conditions are verging on the catastrophic," the group said in a prepared statement. Aurelie Dupont, emergency coordinator for Doctors Without Borders in Awerial, said the situation for women and children who've fled their homes with few belongings was alarming. "There is no clean water, no food, and no place to shelter or sleep," she said. They are relying solely on the help of the local population. A report submitted to the African Union council meeting said the situation on the ground remains "very volatile," amid worsening ethnic tensions. "There are reliable reports that a large number of civilians died in a series of selective killings in Bor town, in Jonglei State, and Bentiu town, in Unity State, that looks very much like an ethnic pogrom," it said. CNN's Arwa Damon and Antonia Mortensen in Juba, and Nana Karikari-apau contributed to this report.