The president of South Sudan, Salva Kiir, has expressed concern about recent strife in his country, condemning those "who would like to take power by force of arms."
Deploring the killings of innocent people, he criticized those "who are targeting others because of their tribal affiliation."
In a written statement, the South Sudanese leader said he has ordered the country's security forces "not to harrass civilians in any way... threaten or abuse them."
"Those unruly and undisciplined soldiers who are behind such terrible acts" he called criminals who "will not escape the long arm of justice."
Kiir called on everyone involved to "put the interest of our newly independent nation first." Mentioning his former vice president and nemesis, Riek Machar, by name, he urged him and forces supporting him to do the same.
Meanwhile in New York, the United Nations Security Council has voted to increase the size of its peacekeeping force in South Sudan, where violence between government forces and breakaway factions has escalated over the past week, endangering hundreds of thousands of civilians, and bringing the new nation to the brink of civil war.
In a statement following the Security Council vote, U.N. Secretary-General Ban Ki-moon thanked leaders across Africa and around the world for their determination to respond to the violence in South Sudan. "The world is watching and the world is acting," he said.
The Security Council resolution authorizes the U.N. to send an additional 5,500 peacekeeping troops to the strife-torn nation, boosting the number of peacekeepers there to 12,500.
Still, Ban warned that the situation remains tense. Two U.N. peacekeepers and hundreds of civilians have been killed over the past week.
Ban expressed concern that the violence may be spreading.
"We have reports of horrific attacks, including extrajudicial killings, rape and mass graves. Tens of thousands have fled their homes and the numbers keep growing and, of course, innocent civilians are being targeted because of their ethnicity," said Ban.
The fighting that followed an alleged coup attempt last week has displaced more than 80,000 people amid reports of violence between members of the Dinka and Nuer ethnic groups. President Salva Kiir, a Dinka, blames former vice president Riek Machar, a Nuer, of masterminding the alleged coup attempt.
Ban warned that those responsible for human rights violations and crimes against humanity will be held accountable, but he added that the political players within South Sudan bear ultimate responsibility for ending the conflict.
"In this season of peace, I urge the leaders of South Sudan to act for peace, stop the violence, start the dialogue [and] save your proud and newly independent country," said Ban.
The immediate prospects for dialogue between the warring parties seem remote. Meanwhile, U.S. President Barack Obama has moved 150 Marines to Djibouti to facilitate the evacuation of Americans in South Sudan. He has indicated that, if necessary, the United States might take "further action."
Reporting from New York by Adam Phillips.
Members of the South Sudan rebel delegation attend the opening ceremony of South Sudan's peace negotiations, Addis Ababa, Ethiopia, January 4, 2014.
Taban Deng Gai, left, head of the rebel delegation and South Sudan's leader of the government delegation, Nhial Deng Nhial, attend the opening ceremony of South Sudan's peace negotiations, Addis Ababa, Ethiopia, January 4, 2014.
Unidentified members of the delegation from the South Sudan government and western observers meet at the Sheraton Hotel, Addis Ababa, Ethiopia, January 4, 2014.
A displaced mother and her baby, one of the few to have a mosquito net, wake up at a refugee camp, Awerial, South Sudan, Jan. 2, 2014.
A young displaced girl carries a bucket of water back to her makeshift shelter at a United Nations compound. The compound has become home to thousands of people displaced by the recent fighting, Juba, South Sudan, Dec. 31, 2013.
Displaced people gather inside a mosquito net tent as they flee from the fighting between the South Sudanese army and rebels in Bor town, in Juba, South Sudan, Dec. 30, 2013.
A displaced woman hangs up laundry on the plastic sheeting wall of a latrine at a United Nations compound, Juba, South Sudan, Dec. 31, 2013.
Yared, 2, is held by his mother, Madhn, who fled from the town of Bor a few days ago. She receives medicine for her child at a Medecins Sans Frontieres (MSF) medical tent, at a United Nations compound, Juba, South Sudan, Dec. 31, 2013.
A young displaced boy rests on the wheel arch of a water truck while others fill containers from it, at a United Nations compound, Juba, South Africa, Dec. 31, 2013.
A family makes tea outside their makeshift shelter at a United Nations compound, Juba, South Sudan, Dec. 31, 2013.
A general view of a camp for displaced people set up in a United Nations compound in Bor, South Sudan, Dec. 25, 2013.
South Sudan army soldiers hold their weapons as they ride on a truck in Bor, Dec. 25, 2013.