United Nations Secretary General Ban Ki-moon has asked the Security Council to send 5,500 more peacekeepers to South Sudan as soon as possible, to protect civilians from worsening violence.
The Security Council is due to vote Tuesday afternoon on a resolution to transfer troops from other U.N. missions in Africa.
The U.N. push comes as the United States increased its diplomatic efforts to calm the increasing ethnic violence in South Sudan, while also repositioning U.S. troops in the region in case they are needed.
U.S. special envoy for South Sudan Donald Booth met Monday with South Sudan President Salva Kiir and had what he called a "frank and open discussion." Booth told reporters by telephone that President Kiir is willing to begin talks aimed at ending the violence with his former vice president Riek Machar.
Mr. Kiir, an ethnic Dinka, has said that an attempted military coup triggered the violence and that Machar, an ethnic Nuer, has been blamed for it.
Machar has been in hiding since President Kiir accused him of leading a coup attempt on December 16. Clashes since then have killed hundreds of people and displaced at least 60,000 others.
Journalist Hannah McNeish, who is in the capital, Juba, tells VOA the fighting has a clear ethnic element, with members of the Nuer and Dinka ethnic groups targeting each other.
"There are people going house to house, tracking people down in term of ethnicity. They are taking them out of their houses, they are binding their hands, and executing them if they are not the right ethnicity. This is completely out of control."
Soldiers believed to be allied with Machar have taken over the capitals of South Sudan's Unity and Jonglei states.
In an interview with VOA South Sudan army spokesman Phili Aguer said troops will retake those towns.
"Definitely the army will recontrol these areas. It's a matter of days and the army will control Jonglei state, and we will work for the re-establishment of the full control of the national army over South Sudan."
The spokesman also accused fighters backing Machar of shooting at a U.S. aircraft that was evacuating citizens from Bor on Saturday. The U.S. military did not identify the shooters, but said four of its personnel were injured.
U.S. President Barack Obama said Sunday he "may take further action" to protect Americans in South Sudan.
Mr. Obama is on vacation in Hawaii, but he said in a letter to congressional leaders that about 46 U.S. troops were deployed Saturday to help with the evacuation. That is in addition to 45 troops deployed to reinforce the U.S. embassy in Juba.
The U.N. secretary-general called on South Sudan leaders to find a "political means" to address the conflict, saying the continued violence poses a "dangerous threat" to the future of the young country.