Rape and cannibalism in South Sudan, African Union says
The African Union (AU) has accused government and rebel forces in South Sudan of extreme violence since the conflict erupted at the end of 2013.
A commission of inquiry found evidence of killings, torture, mutilations and rape, mostly against civilians, as well as episodes of forced cannibalism.
However, it specified that genocide had not been committed during the conflict.
Tensions remain, with a peace deal agreed between the government and rebels in August repeatedly broken.
Tens of thousands of people have died and another two million people have been forced from their homes since the civil war began nearly two years ago.
BBC South Sudan Analyst James Copnall
The gruesome accounts of abuses will grab the headlines, but the AU report also contains two conclusions which will make particularly difficult reading for President Salva Kiir.
The first: the AU Commission did not believe his account of an attempted coup against him which sparked the conflict: "From all the information available to the Commission, the evidence does not point to a coup."
The second: the subsequent killings of Nuer soldiers and civilians in Juba were "committed pursuant to or in furtherance of a state policy" as part of "an organized military operation".
The report also discusses the what has long been claimed by President Kiir's opponents: that the massacres in Juba were carried out, in part, by a militia drawn largely from the president's ethnic group, created before the crisis.
It should not be forgotten that Riek Machar's forces are accused by the AU of terrible and terrifying abuses too.
But the fact that the AU body rejects President Kiir's coup claim, and holds his forces responsible for organised killings in the very first days of the war, will shape how the rest of the world and future generations allocate blame for the conflict.
In its report, the AU said the commission, formed last year under the chairmanship of Nigeria's ex-president Olusegun Obasanjo, had identified perpetrators of violence from both sides.
It documented details of brutal killings, abductions of woman and sexual violence among other abuses, mostly committed against civilians who were not taking part in the fighting.
"The commission believes that war crimes were committed in Juba, Bor, Bentiu and Malakal," the report said in reference to the key conflict towns.
Some witnesses in the capital, Juba, told commission members that they had seen people forced to drink the blood and eat the flesh of people who had just been killed.
They spoke of seeing the perpetrators "draining human blood from people who had just been killed and forcing others from one ethnic community to drink the blood or eat burnt human flesh".
The report also said that mass graves had been discovered by AU investigators.
The commission is urging an internationally backed, African-led court to bring to justice those responsible for the violence.
Despite the seeming ethnic nature of the conflict, the commission said it found no reasonable evidence to prove that genocide had been committed.
Those who committed the atrocities detailed in the report should be brought to justice, presidential spokesman Ateny Wek Ateny told BBC News.
However, he said there was "inconclusive evidence" that his government was involved, and it was an allegation he "cannot accept".
"I'm not categorically denying that there are limited violations that individuals might have inflicted," he said, adding those responsible would be "brought to book". However, he denied there were any government-sanctioned human rights violations.
"It is not sanctioned by the government, it is the individual that might have taken the law into their own hands," he said.
He said South Sudan will form its own commission of inquiry to investigate.
South Sudan's elusive peace:
- At least seven ceasefires agreed and broken since conflict started in December 2013
- Nearly one in five South Sudanese displaced by the current conflict, from a total population of 12 million
- Former rebel leader Salva Kiir became president of South Sudan, the world's newest state, when it gained independence in 2011
- South Sudan has been at war for 42 of past 60 years
The United Nations has already accused the government and rebel fighters of atrocities and crimes against humanity, and says the situation has only worsened since a peace deal was signed in August.
The conflict was triggered by a political power struggle in December 2013 between President Salva Kiir, an ethnic Dinka, and his rival and former Vice-President Riek Machar, a Nuer.
But it quickly took on a bloody, multi-ethnic dimension right across the country.
The AU report seemed to dismiss claims that there had been a coup attempt by Mr Machar, instead finding that the unrest began after government-organised killings of ethnic Nuer civilians and soldiers.