Mass graves have been discovered in South Sudan with evidence of horrific crimes against civilians including forced cannibalism, according to 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.