Shocking stories from North Koreans who have escaped the country have been documented in 400 pages of testimony released by a UN-mandated human rights panel on Monday.
Among the most shocking stories were those from the "kwanliso" political prison camps, evoking the darkest chapters of world history, AFP reported.
"One of the witnesses from one of the camps told of how his duties included gathering up the bodies of those who had died of starvation and putting them in a pot and burning them," said the commission's chair, Australian former top judge Michael Kirby.
The ex-inmate then took the ash and remaining body parts to be used as fertiliser in nearby fields.
Barred by Pyongyang, the commission based its report on testimony from 320 North Korean exiles - dubbed "human scum" by Pyongyang.
Prisoners were also used for martial arts practice, forced to have abortions if they became pregnant, and lived on rodents and leaves.
The report also pointed to allegations that political prisoners were killed in medical experiments conducted to test the impact of chemical and biological weapons.
The report detailed the use of public executions with machine guns, with entire school classes brought to watch.
"At the age of nine, Mr Kim Hyuk witnessed his first public execution," it said.
Another witness, Choi Young Hwa, was aged 16 when he saw a factory manager shot for "espionage" after dismal economic performance.
"He remembered being afraid and thinking that anyone could become a victim of such executions," the report said.
Factory workers were also taken to watch such killings.
Another inmate, a woman, talked about her time in a prison camp for nine years.
If she was late, her food for the day was cut.
Even when she had a broken bone, she had to get up and run, to get to work on time. Work started at 4.30am.
At the camp, she was ordered to cut 800kg of grass. When she was trying to weed, she came across a lot of snakes. She said she skinned the snakes and ate them raw.
She said her family cooked snakes and mice to feed babies. When they were able to have a mouse, it was a special day for them.
She told the commission that they ate things raw, every type of meat they could find. Anything that flew, anything that crawled.
Even the grass that grew in the field, they had to eat.
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