Ethnic groups in South Sudan have fought each other over cattle - a vital part of the indigenous economy - for centuries. But the numbers of deaths are increasing after decades of civil war left the territory awash with small arms.

Analysts say South Sudan, which became independent on July 9, risks becoming a failed state if it cannot control insurgencies and blood feuds that divide its tribes.

The UN spokesman said violence between the Murle and Lou Nuer tribes broke out on August 18.

"There were around 28 casualties at one location and 30 at another site. We also witnessed a number of burned Tukuls (huts)," he told Reuters by telephone.

Reuters