The United Nations says it has unconfirmed reports that hundreds of people have died in clashes between rival South Sudan army factions.
UN diplomats say they have been told by sources in the capital, Juba, that the death toll was between 400 and 500.
There have been two days of clashes in the country following a reported coup attempt against President Salva Kiir, the BBC reports.
The UN Security Council said the clashes are apparently along ethnic lines and there is "potential" for a civil war. Its president, Gerard Araud, said 20,000 thousand people have taken refuge in UN compounds around Juba and the UN is rapidly running out of food and medical supplies.
President Kiir has blamed the clashes on an attempted coup. The government said 10 senior political figures have been arrested. They include Former Finance Minister Kosti Manibe, former Justice Minister John Luk Jok and former Interior Minister Gier Chuang Aluong. Many were members of the cabinet which was sacked in July this year.
Five other prominent figures, including former Vice-President Riek Machar are being sought.
More than 60 soldiers are reported to have been killed in the clashes, which began on Sunday night at a meeting of ruling party the Sudan People's Liberation Movement.
Fresh gunfire was reported on Tuesday near the presidential palace and in other parts of Juba. A curfew is in place in at night.