A United Nations official in South Sudan says 200 people have been wounded in ongoing clashes between rival tribes in the country's largest state.

Toby Lanzer, the U.N. humanitarian coordinator in South Sudan, issued a statement late Sunday that the most critically wounded were now being treated in the capital of Jonglei state, where there is a rebel insurgency against the central government.

South Sudan's army spokesman, Col. Philip Aguer, said the Murle and Lou Nuer tribes constantly clash over cattle thefts, conflicts that date back to the colonial era.

Lanzer's statement said violence in Pibor County in Jonglei caused thousands to flee into the bush.

Sudan, which celebrated its second independence anniversary last week, has been plagued by a border conflict with neighboring Sudan as well as tribal violence.