The United Nations says tribal fighting in South Sudan's Jonglei state has killed at least 600 people since Thursday.

The U.N. mission in South Sudan said Monday there are unconfirmed reports that at least 750 others have been injured.

South Sudanese officials say the fighting stems from a cattle dispute between the Murle tribe and the Lou-Nuer tribe. The two tribes often clash over cattle and land.

A representative for U.N. Secretary-General Ban Ki-moon said Monday that the cycle of violence must stop, and called for reconciliation efforts.

South Sudan became the world's newest independent country last month, after voting to split from the north.

The new country has been plagued with tribal violence and clashes between the government and rebel militias.

The government has urged South Sudanese to work together, saying the country has the potential to become the breadbasket of eastern Africa.