North Korean leader Kim Jong Un’s mistreatment of political prisoners is at least as egregious as that carried out in World War II concentration camps, according to a former international judge who survived Auschwitz.

Thomas Buergenthal, a law professor who served for a decade as an International Court of Justice judge, said a new report he helped write documenting atrocities in North Korea’s prisons shows the Kim regime may be “even worse” than Nazis.

“I believe that the conditions in the [North] Korean prison camps are as terrible, or even worse, than those I saw and experienced in my youth in these Nazi camps and in my long professional career in the human rights field,” Buergenthal, who endured the Auschwitz and Sachsenhausen concentration camps a child, told The Washington Post.

Buergenthal is an author of a report published Tuesday by the International Bar Association, ”Inquiry on Crimes Against Humanity in North Korean Political Prisons.” It documents atrocities inside the country’s prisons, where an estimated 80,000 to 130,000 people are being held.

The report is based on testimony from North Korean defectors, including a former prison guard, and scholarly research, videos and transcripts. It says investigators found evidence of crimes against humanity that have been committed in the prisons, including murder, extermination, enslavement, forcible transfer, imprisonment, torture, sexual violence, persecution and enforced disappearances.

The report focuses on North Korea’s four “total control zones,” where people are sent with no prospect of release. “Hundreds of thousands of political prisoners have been sent to political prisons over the past 50 years, with up to three generations of families detained together and forced into slave labor, mostly to work in mines, logging and agriculture,” the report says.

Prisoners are regularly tortured and killed, according to the report. It says rape is rampant, as is malnutrition, starvation and overwork.

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“There is not a comparable situation anywhere in the world, past or present,” Navi Pillay, another report author who also is a judge in South Africa, told the Post. “This is really an atrocity at the maximum level, where the whole population is subject to intimidation.”

The report calls for an international tribunal to investigate North Korea’s crimes against humanity and to hold accountable those responsible, including Kim, party officials, prison guards and security officials.

“Given North Korea’s tightly controlled leadership structure, Kim Jong Un and his inner circle warrant prosecution under the principle of command responsibility,” the report says.

The study serves as an unofficial update to a 2014 United Nations inquiry on human rights abuses in North Korea, the International Bar Association said.

The North Korean regime’s policy of detaining people it views as enemy “seeds” dates back to the 1950s. But accurately documenting crimes inside the country’s prisons has been hampered by North Korea’s isolation, even as it develops a nuclear arsenal.

President Donald Trump has responded to the nuclear program with bellicose threats and demands that China take responsibility, as one of North Korea’s few allies. China will reportedly open refugee camps on its border with the rogue regime to house defectors.

Also on HuffPost

Local women rest in an alley in Tumangang, North Korea, on Aug. 19, 2015.

A customs officer checks a passenger's camera on a train from Moscow to Pyongyang at the Tumangang railway station.

A customs officer checks a passenger's mobile device.

A general view of the village.

Children walk to school on Aug. 20.

A child rests in the village.

"There are nearly no fat people, everyone was thin," photographer Xiaolu Chu says.

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This article originally appeared on HuffPost.