South Sudan became Africa’s newest nation in July after a referendum agreed under a 2005 peace deal with Khartoum ended decades of civil war that had killed two million people.
But the government in Juba has been struggling to assert its authority over a country roughly the size of France and end tribal and rebel violence in which thousands died last year.
About 60,000 people were displaced last week when armed men of the Lou Nuer tribe attacked settlements of the rival Murle tribe, according to the United Nations.
South Sudan government spokesman Barnaba Marial Benjamin said some Murle members on Sunday attacked two settlements near Akobo in Jonglei state.
“This is in Lou Nuer territory. The Murle were behind their lines,” he said.
Jonglei state governor Kuol Manyang said at least 22 people were killed and 23 wounded in the town of Deng Jok near Akobo in Jonglei.
In a separate attack on Kaikuin village in the same area two women were killed and cattle stolen, he said.
“I don’t have final information on casualties. Details are still unclear,” Manyang said, adding: “Today it was quiet.”
The violence came as the U.N. was trying to supply 60,000 refugees in the Murle area with food, shelter and medical assistance.
“It’s a race against time,” said Lise Grande, U.N. Humanitarian Coordinator for South Sudan, adding the U.N. only has one helicopter to fly in food for people scattered across a vast and remote territory.
About 16,000 people were returning to the town of Pibor which came under attack by Lou Nuer a week ago, while others were going back to destroyed homes, she said.
The government in Juba has declared Jonglei a disaster area.
Some analysts say South Sudan might become a failed state as the government struggles to end tribal and rebel violence, widespread corruption and build up state institutions.