UN chief Ban Ki-moon has urged the Security Council to add 5,500 UN troops to the 7,000-strong force in South Sudan, amid escalating fighting there.
His plea comes as new details emerge of alleged ethnic killings committed during more than a week of violence.
Ban warned that anyone responsible for abuse would be held to account.
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.
The United States has increased its diplomatic efforts to calm the increasing ethnic violence in South Sudan, while also repositioning 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.
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.
Soldiers believed to be allied with Machar have taken over the capitals of South Sudan\’s Unity and Jonglei states.
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.
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.
Source: VOA and agencies