South Sudan's rebel commander Riek Machar has said his forces were not behind the massacre of hundreds of people in the contested town of Bentiu.
The UN has accused them of killing more than 200 people in one mosque alone after driving government forces from the town last week. Video shot by Al Jazeera shows bodies littering the streets of the town and the inside of the mosque.
Machar, who was dismissed as vice president by President Salva Kiir in July 2013, told Al Jazeera on Tuesday that his rebels would not kill their own people.
"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 said.
Al Jazeera's Anna Cavell, who travelled to Bentiu, said the conflict in South Sudan had taken on a new ethnic dimension.
|Al Jazeera's Anna Cavell reports on the massacre
She said many people at a United Nations base in Bentiu, the capital of oil-producing Unity state, were reluctant to speak to journalists for fear of reprisals.
"Different groups from the Dinka and Nuer of South Sudan as well as Darfuris and Misseriya Arabs from Sudan live in Bentiu, so the conflict has now taken on an ethnic dimension, and people are now looking at their neighbours very differently."
UN investigators said that hundreds of civilians were killed because of their ethnicity after rebel forces seized the town last week. The UN Mission in South Sudan condemned what it called "the targeted killings of civilians based on their ethnic origins and nationality''.
Thousands of people in South Sudan have been killed in violence and more than one million people have been forced to leave their homes since December when pro-Kiir troops and those loyal to Machar began to fight along ethnic lines after Machar was accused by Kiir of a failed coup.
Toby Lanzer, the UN's representative, 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 UN base."
"We had 5,000 civilians a week ago in our base, now we have 22,000. We have just one litre of portable water per person for today. It is hard to believe that just a few months ago South Sudan was at peace."
South Sudan's foreign minister, Barnaba Marial Benjamin, told Al Jazeera on Tuesday that he believed Machar's rebels were responsible for the Bentiu killings. "These are his rebels. He has said ... his forces are in control so he has to answer for it", said Benjamin.