In Warrap state, 29 people were killed after an attack on Monday by rebels led by Peter Gadet, a former southern general turned militia commander.
"These people were killed in an attack by those rebels of Gadet, coming from Unity state, and the dead included two police officers," said Philip Aguer, southern army spokesman.
The southern army has battled at least seven different rebel militia groups in recent months, with the scale of violence raising concern for the plight of civilians, as the region gears up for independence due in less than a month.
Meanwhile, separate battles between heavily armed cattle raiders last week have left at least 71 people dead in Lakes state, local officials there said.
Deadly clashes over livestock between south Sudan's Toposa tribesmen and the Kenyan ethnic Turkanas in a remote area of the countries' shared border were also reported today.
Clashes over cattle are common in south Sudan and Kenya's remote north, where herders are often armed.
