Mass graves have been discovered in South Sudan with evidence of horrific crimes against civilians including forced cannibalism, according to a report by the African Union.
The report also disputes there was a coup attempt in December 2013 by former vice president Riek Machar.
The African Union investigators, led by former Nigerian president Olusegun Obasanjo, found that the conflict began with a skirmish between members of the presidential guard in the capital Juba, followed by the government-organised killings of ethnic Nuer civilians and soldiers.
President Salva Kiir is a Dinka while Mr Machar is a Nuer.
Hundreds of Nuer men were rounded up and shot, and the report said perpetrators also tortured their victims, including by forcing them to eat human flesh.
The report was scheduled for release months ago but its publication was delayed by the African Union's Peace and Security Council.
It found that the killings were “an organised military operation that could not have been successful without concerted efforts from various actors in the military and government circles”.
The report added: “Roadblocks or checkpoints were established all around Juba and house to house searches were undertaken by security forces. During this operation male Nuers were targeted, identified, killed on the spot or gathered in one place and killed.”
Defence minister Kuol Manyang Juuk described a shadowy "group (that had) organised itself as Rescue The President. It killed most people here (in Juba) — from (December) 15th to 18th. It was even more powerful than organised forces."
The group comprised some Dinka soldiers who had been mobilised following a 2012 border crisis with northern neighbour Sudan.
Some of these soldiers were moved south to Mr Kiir’s private farm near Juba in 2013 and later participated in the killings, the report said, citing interviews with informants.
Amid the Juba killings, Mr Machar fled the capital and mobilised an insurgency which committed revenge attacks against the Dinka, sparking a cycle of violence which also included rape and the murder of people in churches and hospitals, according to the report.
Those revenge attacks occurred so quickly that they were also likely to have been co-ordinated, it added.
Mr Kiir and Mr Machar signed a peace agreement in August but fighting continues.
PA