South Sudan says massacre toll up to 400

South Sudan’s government said the death toll from a sectarian massacre last week now exceeds 400, while the United States called the targeted killing of hundreds of civilians an "abomination" and appealed to opposition forces and government leaders to condemn those responsible and bring them to justice.

Michael Makuei, South Sudan’s Minister of Information, said Wednesday that the killings in Unity state in the city of Bentiu were carried out by fighters who have battled the government in months of fighting after President Salva Kiir accused his former vice president, Riek Machar, of an attempted coup last year.

United Nations investigators said Monday that hundreds of civilians were killed because of their ethnicity after opposition forces seized the town last week. The U.N. Mission in South Sudan condemned what it called "the targeted killings of civilians based on their ethnic origins and nationality.”

The Obama administration, meanwhile, was unequivocal in its condemnation of the violence. According to the U.N., thousands of people have been killed in violence since December and more than one million people have been forced to leave their homes.

"We are horrified by reports out of South Sudan that fighters aligned with Machar massacred hundreds of innocent civilians last week in Bentiu," White House Press Secretary Jay Carney said in a news release.

"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 said.

Al Jazeera correspondent Anna Cavell, who visited Bentiu, said the murders appeared to be along sectarian lines – part of the overall fighting that continues unabated between troops loyal to President Kiir, an ethnic Dinka, and forces tied to Machar, an ethnic Nuer and the country’s former vice president.

Despite the allegations of a rebel massacre, however, Machar denied that his men had carried out the attack and blamed forces loyal to Kiir.

"I contacted the field military commander in Bentiu who told me that such accusation is false. First of all we respect our people, and the majority of the forces are from the region and we can't kill our citizens," Machar told Al Jazeera on Tuesday.

Toby Lanzer, the U.N.'s representative in South Sudan, told Al Jazeera on Monday that people "associated with the opposition" had used an FM radio station to broadcast hate speech in the town.

"With hate speech and violence continuing as they are, we're going to have an even greater catastrophe on our hands at the end of this year," he said. "I think the saddest testament to the current situation is that we have had members of all communities, even those accused of perpetrating these crimes, fleeing to the U.N. base."

Al Jazeera and The Associated Press