South Sudan President Salva Kiir denied allegations by the United Nations that ethnic cleansing in the country's conflict is so bad that the stage is set for genocide.
A UN commission on human rights in South Sudan said a steady process of ethnic cleansing was under way in the country, involving massacres, starvation, gang rape and the destruction of villages.
On Wednesday, three commission members who had travelled around South Sudan for 10 days said they observed deepening divisions in a country with 64 ethnic groups.
However, President Kiir strongly denied the allegations on Thursday.
"There's no such thing in South Sudan. There's no ethnic cleansing," he told Reuters news agency in the South African city of Johannesburg.
Security guards prevented further questions.
More than one million people have fled South Sudan since the conflict erupted in December 2013 after Kiir fired Riek Machar as vice-president.
It is the largest mass exodus of any conflict in central Africa since the 1994 Rwandan genocide.
The fighting has mostly pitted Kiir's Dinkas, the dominant ethnic group estimated to be roughly one-third of the population, against Machar's Nuer tribe.
But as fighting has spread to southern border states, known as Greater Equatoria, it has sucked in dozens of other ethnic groups that are also historically in conflict with the Dinka.
More than 4,000 people have been crossing daily into Uganda, where the Bidibidi refugee settlement, open since August, now hosts some 188,000 people.
Another 36,600 refugees have reached Ethiopia since early September, and more than 57,000 fled to Congo this year.
"We don't have sufficient means to help them," said Medard Mokobke Mabe, coordinator for the Red Cross in DRC's village of Karukwat, estimating more than 100 refugees arrive each day.
"There isn't food to eat."
Casie Copeland, a researcher with the International Crisis Group, said the world had turned a blind eye to the fighting in its newest country, whose independence from Sudan in 2011 was strongly backed by the United States and other Western nations.
"From the war's outset, the UN never tried to maintain a death toll," she said.
"Guesses vary from 50,000 up to 300,000. It demonstrates a shocking lack of humanity that no one has tried to establish the scale of violence."
UN spokesman Farhan Haq said its mission in South Sudan had faced numerous challenges accessing affected areas, but was doing all it could to establish death tolls and other human rights violations.
Chairman of the commission that travelled to South Sudan, Yasmin Sooka, told a news conference there was "already a steady process of ethnic cleansing under way in several areas of South Sudan using starvation, gang rape and the burning of villages".
"The stage is being set for a repeat of what happened in Rwanda and the international community is under an obligation to prevent it," she said.
Sooka then told Al Jazeera there were "so many different groups of armed actors, including the military who are talking about dealing with a rebellion and putting it down".
"You have ethnic tensions because people have been displaced from their land based on ethnicity. Everybody believes that a military conflict is almost inevitable in different parts of the country," she said.
Sooka described the amount of rape committed by all armed groups in the country as "mind-boggling".
"Aid workers describe gang rape as so prevalent that it's become 'normal' in this warped environment. But what does that say about us that we accept this and thereby condemn these women to this unspeakable fate?"