Around 10,000 South Sudanese refugees have fled north into Sudan, as hundred of thousands remain displaced in the nearly month-long conflict.
The United Nations refugee agency Sunday said thousands more are sleeping and cooking in the open at a camp in Turalei, northern South Sudan.
The crisis in South Sudan, the youngest country in the world, started after President Salva Kiir dismissed Vice President Riek Machar.
Mr. Kiir, who is an ethnic Dinka, accused Machar, who is an ethnic Nuer, of trying to overthrow the government.
Machar denies the accusation, and accuses the government of crushing political opponents.
Meanwhile, negotiators continue to press the two sides to agree to a cease-fire at peace talk being held in Ethiopia.
Machar's demand for the release of detainees remains a stumbling block to a deal aimed at halting violence.
Although both sides have held talks in recent days in Addis Ababa, there has been little progress after Mr. Kiir refused to release 11 detainees arrested in December in an alleged coup plot.