South Sudanese army soldiers killed as many as 16 people in a town near the Ugandan border, witnesses said.
Hundreds of locals fled into Uganda following Monday's violence in the town of Parjok.
Witnesses said men wearing uniforms of the South Sudan army arrested more than 10 young people and executed them.
A deputy spokesman for the army, Brigadier General Santo Dominic, said the troops had killed people whom he described as "bandits."
The general told VOA's South Sudan in Focus that his forces had gone on the attack after he received reports that bandits were looting buildings and killing civilians.
Lam Paul Gabriel, deputy spokesman for the rebel SPLM-IO, said it was the soldiers who did the looting and killing. He said a community leader who went to rescue students trapped in a primary school was shot and killed by the army.
"They also went to a health unit and found a health worker, and he was slaughtered," Gabriel said. "They grabbed everything from the school, they destroyed the hospital completely, especially in the market center, and they destroyed all the shops and looted everything from the shops."
Both Dominic and Gabriel said 16 people had been killed.
Governor plans visit
Tobiolo Alberio Oromo, governor of Imotong state, said he didn't have enough information to report casualty figures, but he confirmed that South Sudanese troops were in Parjok conducting military operations.
"I received a call from one of the community leaders on the ground, and [he] informed me that there is fighting on the ground," he told VOA. "Then this morning I managed to get information, and they say the situation needs the state government to come in."
The governor said he was planning to visit the area to assess damages and determine what happened in Parjok.
"I want to make sure that I go to the area, and if people have fled the area, they must come back as well, as to ensure humanitarian workers assess the situation," he said.
Violence associated with South Sudan's three-and-a-half-year civil war has driven more than 1.6 million people out of the country, according to the latest statistics from the U.N. refugee agency. More than 750,000 are living in Uganda.