GENEVA  - The United Nations on Friday said it is launching a massive humanitarian operation to help an estimated 50,000 people hit by inter-ethnic conflict in South Sudan's Jonglei state.

"The United Nations is launching a massive humanitarian emergency," said the media spokeswoman for the Office for the Coordination of Humanitarian Affairs (OCHA), Elisabeth Byrs on Friday.

The programme is aimed at helping thousands of people to return home after clashes between the Lou Nuer and Murle communities, OCHA said.

During the last 72 hours, UN experts have assessed the situation in Pibor Likuangole, Boma and Walgak.

"The needs are great, of course," Byrs said. "It is currently estimated that 50,000 people are affected by violence in the region" of South Sudan.

"Thousands of people now need food, water and shelter. Aid agencies are assessing their needs," Byers added.

"The situation in humanitarian terms is grim," said UN Humanitarian Coordinator Lise Grande via video link.

A top local Sudanese official said more than 3,000 people were killed in brutal massacres last week.

"There have been mass killings, a massacre," said Joshua Konyi, commissioner for Pibor county in Jonglei state.

"We have been out counting the bodies, and we calculate so far that 2,182 women and children were killed and 959 men died." United Nations and South Sudanese army officials have yet to confirm the death tolls and the claims from the remote region could not be independently verified.

If confirmed, the killing of 3,141 people would be the worst outbreak of ethnic violence ever seen in southern Sudan, which became a separate nation after splitting from Khartoum in July.

A column of some 6,000 rampaging armed youths from the Lou Nuer tribe last week marched on the remote town of Pibor, home to the rival Murle people, whom they blame for abductions and cattle raiding and have vowed to exterminate.

The Lou Nuer attacked Pibor at the weekend, torching huts and looting a hospital, and only withdrew after government troops moved in.

More than 1,O00 children are missing, feared abducted, while tens of thousands of cows were stolen, added Konyi, who is himself an ethnic Murle.