30 December 2011 Last updated at 13:07 GMT
Cattle are a central part of the lives of many communities in South SudanThe United Nations has moved a battalion of combat troops to the South Sudanese town of Pibor to prevent an attack by the Lou Nuer ethnic group.
Tens of thousands of people from the rival Murle group have fled the town in the last few hours, fearing an attack.
Inter-ethnic clashes in Jonglei state have cost the lives of around 1,000 people in recent months, in violence that was initially triggered by cattle raids.
Most victims are women and children.
Both communities have abducted children during the violence.
About 6,000 armed men from the Lou Nuer community are marching through Jonglei state burning homes and seizing cattle along the way, says the BBC’s Will Ross, reporting from Nairobi.
Earlier this week an entire town was burnt to the ground by the Lou Nuer fighters. Dozens died on both sides.
The United Nations humanitarian co-ordinator in South Sudan, Lise Grande, told the BBC that the UN was reinforcing its troops in Pibor to assist the South Sudanese army in defending civilians.
“We are very concerned by the scale of this,” she said.
“The UN is facing enormous logistical challenges – we still have no military aircraft, only civilian helicopters,” she added.