More than 16 thousand people have sought shelter after two days of intense fighting in South Sudan's capital, Juba.
Many of the displaced take refuge in a UN compound next to Juba airport.
Aid workers say the number of refugees is rising and food supplies are running low.
The UN says up to 500 people have died in clashes between rival army factions
"You can find a lot of bodies all over the place. I had my cousin over there, he is not even bringing bodies right now. And I had a lot of friends that were out there with them for a couple of days - now they are all gone," a Juba resident said.
Many more people have been wounded as authorities try to regain complete control of the city, after what they say was an attempted military coup by the former Vice-President, Riek Machar.
The Juba government said it had arrested 10 major political figures and was hunting for its former vice president.
U.S. Secretary of State John Kerry, on a visit to the typhoon-ravaged central Philippine city of Tacloban, urged a "peaceful and democratic" solution.
"Political differences need to be resolved by peaceful and democratic means and those have been hard fought for. The government should respect the rule of law and the people of South Sudan should be able to realise their full potential in peace," U.S. Secretary of State John Kerry said.
South Sudan has struggled to achieve a stable government since becoming independent from Sudan in 2011.
Independence was intended to end a decade-long conflict against the north.
But instead the oil-rich country remains ethnically and politically divided.