JUBA - The White House expressed horror at what it called the "abomination" of spiralling violence in South Sudan's civil war, where rebels have been accused of massacring hundreds of civilians.
The rebels seized the town and oil-hub of Bentiu last week, unleashing two days of ethnic slaughter as they hunted down civilians sheltering in mosques, churches and a hospital, butchering dozens on the roadside, according to the United Nations.
"We are horrified by reports out of South Sudan that fighters aligned with rebel leader Riek Machar massacred hundreds of innocent civilians last week in Bentiu," White House spokesman Jay Carney said.
"These acts of violence are an abomination. They are a betrayal of the trust the South Sudanese people have put in their leaders," he said.
"Images and accounts of the attacks shock the conscience: stacks of bodies found dead inside a mosque, patients murdered at a hospital, and dozens more shot and killed in the streets and at a church - apparently due to their ethnicity and nationality - while hate speech was broadcast on local radio," Carney added, noting the dead have been buried in mass graves and populations of camps for displaced persons have surged.
The UN said the killings continued for almost two days after the rebels issued a statement boasting of victory in Bentiu, a time when rebel spokesman Lul Ruai Koang previously said gunmen were "mopping and cleaning up" in the town.
South Sudan's army has been fighting rebels loyal to sacked vice president Riek Machar since the unrest broke out more than four months ago.
The conflict has taken on an ethnic dimension, pitting President Salva Kiir's Dinka tribe against militia forces from Machar's Nuer people.
The White House called on Kiir and Machar to "make clear that attacks on civilians are unacceptable, perpetrators of violence on both sides must be brought to justice, and the cycle of violence that has plagued South Sudan for too long must come to an end".
However, Koang praised the "gallant forces" of the insurgents, who the UN said were driven by calls over local radio to rape women from the opposition ethnic group and drive out rivals from the town.