The army of south Sudan says 82 people have been killed in fighting between rebel militia and civilians in Warrap state.
Army spokesman Philip Aguer said Tuesday that the clashes broke out when rebels attacked a cattle camp, killing 34 people and wounding 45.
He says the cattle herders later ambushed the militiamen, killing 48 of them.
Aguer said the rebels entered Warrap after troops chased them out of neighboring Unity state last week.
Unrest in south Sudan has raised concerns about the region's stability as the south prepares for independence from the north on July 9.
Hundreds of people have died in clashes involving rebel groups since January, when the south overwhelmingly voted for secession.
The south's ruling party, the Sudan People’s Liberation Movement (SPLM), has accused the north of training and arming militias to destabilize the south. The north's ruling National Congress Party has denied the allegations.
The north and south are attempting to settle several key issues before southern independence, including the fate of the oil-producing Abyei region. Negotiations have not produced significant progress.
The January referendum was part of a 2005 peace deal that ended Sudan's north-south civil war.
Some information for this report was provided by AP, AFP and Reuters.