JUBA/KHARTOUM (Reuters) - The United States issued a rare criticism of South Sudan on Wednesday, saying the African state was failing to protect civilians in the east where the army is fighting an insurgency.
Western powers have long urged Juba to find a peaceful solution to fighting involving the army, a rebel group and rival tribes in the vast Jonglei state but have so far mostly refrained from criticizing the government.
A United Nations source said new fighting erupted a week ago between the rival Lou Nuer and Murle tribes in the Pibor area in Jonglei, killing an unknown number of people.
More violence was expected as armed youths from both sides were amassing forces in the area, the source said. A U.N. team visiting the town said that most civilians had left Pibor, contrary to government figures, the United Nations said in a report.
The United States, South Sudan's biggest ally, said it was "deeply disappointed" that the army, or SPLA, had failed to protect civilians in vulnerable areas in Jonglei.
"The lack of action to protect civilians constitutes an egregious abdication of responsibility by the SPLA and the civilian government," the U.S. embassy in Juba said in a statement.
Washington urged the government to prevent "SPLA attacks on U.N. staff and humanitarian assets". It gave no details but soldiers had looted compounds of U.N. agencies and aid agencies in Pibor in May, according to aid sources.
South Sudan has struggled to turn its army, a loose group of former guerrillas formed the civil war with Khartoum, into a professional force since seceding from Sudan in 2011 under a 2005 peace deal. The U.S. was a driving force in pressuring Khartoum into allowing an independence vote.
The army has faced a rebellion by militia leader David Yau Yau but diplomats say the SPLA is fuelling dissent with abuses such as rape and torture committed during a state disarmament campaign.
A cycle of tribal violence has killed more than 1,600 people in Jonglei since South Sudan's secession, uprooting tens of thousands of civilians and hampering plans to explore for oil with the help of France's Total and U.S. firm Exxon.
Analysts say the roots of the tribal violence and cattle raids go back to South Sudan's failure to start development in Jonglei and elsewhere in the vast country due to corruption.
(Reporting by Andrew Green and Ulf Laessing; Editing by Michael Roddy)