South Sudanese authorities confirmed clashes between the military and rebel groups occurred last week in Jonglei state. A military spokesman confirmed to the independent Sudan Tribune that fighting broke out in the state's Pibor County, though the newspaper reported it was unable to confirm the extent of the casualties.
A U.N. report in June said violence between rival ethnic groups in Jonglei state led to deaths, abductions of women and children, destruction of homes and the displacement of thousands of people.
The report described a "cycle of violence" in the region, near South Sudan's border with Ethiopia.
U.N. delegates visited areas afflicted by conflict alongside members of the Sudan People's Liberation Army, South Sudan's military. The United Nations said delays in SPLA intervention left many civilians vulnerable.
South Sudan gained independence last year under the terms of a peace agreement with Khartoum. Oil disputes, border conflicts and ethnic tensions are threatening the deal, however.