North Korea used South Korean prisoners of war and their descendants through several generations as slave labour in a vast network of coal mines, a rights group said Thursday.
Tens of thousands of South Korean prisoners of war were never returned by Pyongyang after the 1950-53 Korean War.
Instead, they were assigned to toil at coal mines in slave-like conditions, with their children and grandchildren inheriting the brutal fate, according to the Seoul-based Citizens' Alliance for North Korean Human Rights (NKHR).
North Korea's so-called "songbun" system classifies citizens according to their socio-political background, from the loyal "core" to the "neutral" and the "hostile".
"This songbun has been passed down to their children and grandchildren who are bonded to labour in coal, lead, zinc, magnesite and other mines," the report said.
"They are completely restricted from changing residence, job, or attaining higher education."
Pyongyang invaded the South in 1950 and by the time the armistice was signed, hundreds of thousands of captured soldiers were held on both sides of the DMZ.
While the Geneva Convention requires all POWs to be repatriated once hostilities end, Pyongyang returned only 8,343 South Koreans.
A UN human rights report in 2014 concluded that at least 50,000 POWs from the South remained in the North after the war, and that around 500 were still alive.
But their plight was ignored by the Seoul government, the author of the NKHR report, Joanna Hosaniak told AFP.
"There is no knowledge and there is no interest" in the issue in South Korea, she said.
"We are not raising this problem during summits with North Korea, because none of the human rights issues were raised during the summits, whether with President Moon or with President Trump."
Pyongyang insists it protects "genuine human rights" and dismisses accusations of abuses by the international community.
It maintains that all POWs were returned according to the armistice terms, with a government official previously saying that any who remained did so out of a wish "to remain in the bosom of the republic".
Coal was a top export item -- largely to China -- and foreign currency earner for Pyongyang, until its export was banned in 2017 under UN Security Council sanctions imposed over the North's nuclear weapons and ballistic missile programmes.
But an annual report to the UN by independent monitors last year said North Korea earned hundreds of millions of dollars through illicit coal exports in 2019, which "historically contributed to the country's prohibited nuclear and ballistic missile programmes".
Satellite imagery shows continued production at coal mines, independent investigators say, as the country suffers from severe energy shortages.