South Sudan clashes: Murles exact revenge in Jonglei
Some 57 people, mostly women and children, have been killed in a revenge attack in South Sudan, officials say.
Information Minister Barnaba Marial Benjamin said members of the Murle community had attacked their Lou Nuer rivals in Jonglei state.
Earlier this month, a force of some 6,000 Lou Nuer fighters went on the rampage, forcing tens of thousands of Murles to flee their homes.
The two groups have a long history of stealing each other's cattle.
Some 1,000 people have been killed in the past year.
Following the recent clashes, extra UN peacekeepers and soldiers were rushed to the area and Jonglei was declared a disaster zone.
The UN has launched a "massive emergency operation" to help some 50,000 affected people who fled the town of Pibor.
Mr Benjamin said that so many of those killed in the latest attack were women and children because the raid was carried out in the evening and night, when many were asleep in their huts.
Journalist Hannah McNeish, in the South Sudanese capital Juba, says many people are asking why the UN and army have been unable to prevent the latest clashes.
But the UN points out that Jonglei state is the size of Bangladesh and the peacekeepers cannot be everywhere at the same time.
Cattle vendettas are common in South Sudan, as are other clashes between rival groups. The UN says some 350,000 people were displaced because of intercommunal violence last year.
This presents a major challenge to the government of the newly independent state, which also faces cross-border tensions with its northern neighbour Sudan.
South Sudan is one of the world's poorest regions - it gained independence from Sudan in July 2011 and has hardly any roads, railways, schools or clinics following two decades of conflict, which have left it awash with weapons.