JUBA/ADDIS ABABA: African Union investigators discovered mass graves in South Sudan and found evidence of horrific crimes, including forced cannibalism, according to a long-awaited report. President Salva Kiir’s faction in the conflict is also accused of recruiting an irregular tribal force before the outbreak of war in December 2013.

Both the government and rebels in South Sudan carried out war crimes against civilians and should face justice, an African Union human rights investigation has found.

The AU’s Commission of Inquiry on South Sudan lists a string of abuses, including forced cannibalism and dismemberment, according to the report published late Tuesday.

It also presents testimony that the ethnic violence, which began in the capital Juba in December 2013, may have been premeditated.

“There are reasonable grounds to believe that acts of murder, rape and sexual violence, torture and other inhumane acts... have been committed by both sides to the conflict,” the report said.

Government troops carried out organized killings of members of the ethnic Nuer in Juba, the capital, the report said. When violence broke out, Machar, a Nuer, became a rebel leader. He and Kiir, an ethnic Dinka, recently signed a peace agreement.

The African Union investigators, led by former Nigerian President Olusegun Obasanjo, found that the conflict began on Dec. 15, 2013, as a skirmish broke out between Dinka and Nuer soldiers of the presidential guard following political tension between Kiir and Machar, who had been fired as Kiir’s deputy the previous July.

The report was scheduled for release months ago but its release was delayed by the African Union’s Peace and Security Council.

Hundreds of Nuer men were rounded up and shot, and mass graves were discovered. Perpetrators — described as government forces or their allies — allegedly tortured their victims, including by forcing them to jump in fires or eat human flesh, according to the report.

The killings were “an organized military operation that could not have been successful without concerted efforts from various actors in the military and government circles,” the report said.

“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.”

The report said Minister of Defense Kuol Manyang Juuk described a shadowy “group (that had) organized itself as Rescue the President. It killed most people here (in Juba) — from 15th to 18th. It was even more powerful than organized forces.”

The group comprised some Dinka soldiers who had been mobilized following a 2012 border crisis with northern neighbor Sudan. Some of these soldiers were moved south to Kiir’s private farm near Juba in 2013 and later participated in the killings, the report said, citing interviews with informants.