The Pentagon said Marines evacuated about 20 Americans from the U.S. Embassy in Juba.
The warring factions held preliminary meetings Friday in neighboring Ethiopia, mediators said.
Madol, who previously studied at Grand Rapids Community College in Michigan, returned to South Sudan a couple of months ago after hearing his mother was sick. Her health problems are worse now: She was shot and broke a leg in this week's violence in Bor.
"The White Army just took over after everybody left the village. They burned all the huts and they shoot people too during that fight," said Madol, 33, referring to a common name used for the fighters from the Lou Nuer ethnic group.
South of Bor, thousands of families like Madol's have been fleeing to the Nile River region of Awerial. Families are now camping out in the shade below any tree they can find. Aid groups estimate that perhaps between 60,000 and 75,000 people have streamed out of Bor in search of safety from the armed Lou Nuer, a group seen as loyal to Machar.
"It's hard to get medical (treatment) now," said Madol. "All this place is way dirty. All the children are getting dirtier and sick. It's kind of hard to tell how people survived and made it through to this side of the river."
Through the decades of civil war fought between Sudan and its southern region, thousands of "Lost Boys of Sudan" spent years drifting while fleeing bloodshed and famine before landing in other countries like the U.S. Madol was one of those boys. South Sudan peacefully broke away from Sudan in 2011 following a 2005 peace deal that ended a decades-long war. But now fighting has erupted in South Sudan along ethnic lines, ensnaring Madol and many others.
Toby Lanzer, the U.N.'s top humanitarian official in South Sudan, said Friday that the situation around Awerial is difficult.
"We're working to get as much aid to civilians there as possible," he wrote on Twitter. The International Red Cross says Awerial is the "largest single identified concentration of displaced people in the country so far."
Deng Ghai Deng, 19, fled Bor and crossed the Nile with his sister. He said fighting in Bor killed many, and he complained that the displaced families have no safe drinking water, food or shelter.
"Some of the children, even the small kids they are starving in the forest in Jonglei state," he said. "They don't have transport so they can cross the river into Lakes state where I am now. The situation is really very bad. My mum and dad, they are still in Jonglei state, they are still in the forest. They will not come because of money."
The U.S. announced an additional $50 million in funding assistance, including for U.N. programs and the international Red Cross. The international community says at least 180,000 people have been displaced in the fighting. A conservative estimated death toll stands at least 1,000 people.
President Salva Kiir insists the fighting was sparked by a coup attempt mounted by soldiers loyal to Machar on Dec. 15. But that account has been disputed by some officials of the ruling party who say the violence began when presidential guards from Kiir's Dinka ethnic group tried to disarm those from the Nuer group of Machar. From there, violence spread across the country, with forces loyal to Machar defecting and seizing territory from loyalist forces.
South Sudan has been plagued by ethnic tension and a power struggle within the ruling party that escalated after Kiir dismissed Machar as his vice president in July. The rebels back Machar, who is now a fugitive sought by the military.
Dina Mufti, a spokesman for Ethiopia's Foreign Ministry, said the introductory meetings in Addis Ababa, Ethiopia, were necessary to bridge the groups' differences ahead of direct talks expected to start Saturday.
AP reporter Elias Meseret contributed to this report from Addis Ababa, Ethiopia.