Jonglei clashes: South Sudan declares a disaster
South Sudan has declared a disaster in Jonglei state, where some 100,000 people have fled recent clashes between rival ethnic groups.
This would enable aid agencies to move in urgently, as food, medicine and shelter was badly needed, the information minister told the BBC.
Following days of fighting, he said the areas was now under government control.
Some 6,000 ethnic Lou Nuer fighters attacked the area around Pibor town, outnumbering army and UN forces.
This is the latest round in a cycle of violence which has lasted several months - in one incident last year some 600 Lou Nuer were killed by attackers from the Murle community, the group which fled from Pibor.
The clashes began as cattle raids but have spiralled out of control.
There have been some reports that more than 150 people had been killed but Information Minister Mariel Benjamin Barnaba told the BBC's Focus on Africa programme that he could confirm the deaths of between 20 and 30 people.
He said he could guarantee the security of any aid workers who went to the area.
"This area is under the complete control of the government," he said.
On Wednesday, UN humanitarian co-ordinator in South Sudan Lise Grande said that "hundreds, if not thousands" of people had started to return to Pibor.
But she said the humanitarian situation was "pretty grim".
"They've been without food, they've been without water, without shelter."
She rejected criticism of the UN and the South Sudan army - the SPLA - of not having done enough to help civilians, many of whom reportedly faced attack when they fled the town.
"What the United Nations mission has been doing is helping the government to defend the town, we've been rescuing civilians, we've been evacuating civilians and we've been helping to deter violence. The UN has done its job," she said.
An attack on the town's southern flank had been repulsed after the SPLA, backed by UN armoured personnel carriers, had fired at the Lou Nuer, she said.
Besides the looting of a Medecins Sans Frontieres clinic, the town had not suffered much damage and the government was beginning to deploy 3,000 extra soldiers and 800 police officers to the area, Ms Grande said.
Earlier, John Boloch of South Sudan's Peace and Reconciliation Commission and a member of the Murle community, said people who had fled Pibor had since been hunted down and killed near the River Kengen, south-east of the town.
"Children and women were massacred in that area… on the 2nd [of January], up to the 3rd," he told Sudan Catholic Radio News.
He accused local politicians of exacerbating the long-standing rivalries for their own ends and also asked why UN peacekeepers and the army were protecting government buildings in Pibor, rather than people.
There are also reports that many people may have drowned in a river as they fled the attacks.
Mr Barnaba said that leaders of the two communities would be invited to a "peace forum" to discuss how they can put an end to the cycle of violence.
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.