The United Nations has made a plea for peace as talks start between South Sudan’s government and rebels.
Representatives of the two sides are in Ethiopia’s capital, Addis Ababa.
The hope is to work out details of a ceasefire to end more than two weeks of bloodletting which erupted from ethnic tension and a power struggle within the ruling party.
The top United Nations official in South Sudan urged both factions to “give peace a chance”.
UN Mission head Hilde Johnson said: “We have seen terrible acts of violence in the past two weeks, there has been killings and brutality, grave human rights violations and atrocities committed.
“The country is at a crossroads, it’s at a fork in the road but it can still be saved from further, major escalations of violence. It is up to the leaders of this country and the two parties.”
Mediators said they were worried the talks are at risk from clashes around the key town of Bor, around 150 kilometres north of the capital Juba.
Medical charity Medecins Sans Frontieres said 70,000 civilians have fled Bor while the UN counts at least 180,000 people displaced.
The fighting for control of the oil-rich country pits the President Salva Kiir against the man he ousted Vice President Riek Machar.
The violence has divided the country along the ethnic lines of Machar’s Nuer group and Kiir’s Dinkas.
Washington, the United Nations and South Sudan’s neighbours played a central roll in negotiations that ended decades of civil war with Sudan to the north and led to the secession of South Sudan in 2011, and have been scrambling to stem the latest fighting before it escalates.
The White House increased the pressure late on Tuesday by saying it would deny support to any group that seized power by force.
“We will hold leaders responsible for the conduct of their forces and work to ensure accountability for atrocities and war crimes,” said spokeswoman Caitlin Hayden.