The authorities in South Sudan say at least 300 people have been killed and many more injured in the latest wave of intercommunal fighting in Jonglei state, east of the country.
Three aid workers, including one from Médecins Sans Frontières, are among those killed.
Fighting broke out on Saturday between the Murle and Lou Nuer communities. A local elder told the BBC that Murle youths burned down many villages in Uror county before being repulsed.
Health workers say many of the victims have gunshot wounds. Some of the injured have been airlifted to the capital, Juba, for treatment.
The UN Mission in South Sudan has deployed peacekeepers to the area which remains tense. Some people tried to go back to their homes but immediately returned as they feared for their safety.
Authorities say as many as 800 people have been killed since the wave of revenge attacks begun in February.