Clashes between rival army factions in South Sudan have left up to 500 dead and 800 wounded, a top UN official told the UN Security Council on Tuesday.
The United Nations has been told by local hospitals that between 400 and 500 people have been killed in South Sudan's capital since Sunday, UN peacekeeping chief Herve Ladsous told the council, according to diplomats who attended a private briefing with him.
Troops loyal to President Salva Kiir have been fighting rival followers of former vice president Riek Machar. Salva Kiir has accused the rival camp of staging a coup.
Between 15,000 and 20,000 people have sought refuge in UN compounds around Juba, Ladsous was quoted as saying.
Ladsous told the council that the United Nations had not been able to verify the toll given by two hospitals in the capital, Juba.
Security Council president Gerard Araud, France's UN ambassador, said after the emergency consultations that while the number of dead had not been confirmed "there is a heavy toll, it is obvious."
Araud added that fighting had also been reported outside of the capital, in Pibor in Jonglei state which has a history of clashes between rival ethnic groups.
The government said 10 key figures including ex-ministers have been arrested, but that Riek Machar was on the run.
Araud said the fighting appeared to be on ethnic lines. Salva Kiir is an ethnic Dinka while Riek Machar is a Nuer.
A Security Council statement expressed "serious concern" over the fighting that has caused "large numbers of casualties, as well as over the risk of targeted violence against certain communities."
The council called on both sides to "immediately cease hostilities."
UN leader Ban Ki-moon spoke with Salva Kiir on Tuesday and urged him to offer "dialogue" with the opposition. Ban also spoke with the president of neighboring Uganda, Yoweri Musseveni, about the unrest, officials said.
The Security Council also said Salva Kiir's government should hold talks with the opposition.
The Security Council meeting was called at the request of the United States which has ordered non-essential diplomatic staff out of South Sudan.