Some 200,000 political prisoners are being held in concentration camps in North Korea, and some have been executed by shooting or hanging, according to South Korea's National Human Rights Commission.
The commission on Wednesday released a study of conditions in North Korean political prison camps based on testimony from North Korean defectors collected for the commission by the Database Center for North Korean Human Rights last year.
The study says there are six political concentration camps in the North. The first was opened in the 1950s, and the number rose to 13 during the 1970s. Since the 1980s some have been closed.
Prisoners are only ever released from one of the camps, Yoduk in South Hamgyong Province. At the other five they are held for life.
At some of the camps, prisoners act as "capos" administering beatings and torture to fellow inmates. One defector testified that while in a camp, he had witnessed his mother and elder brother publicly executed for attempting to escape.
Seven defectors who were inmates or in command positions in North Korean camps between the 1960s and 2006 were interviewed intensively. Some 322 others questioned fled North Korea between the 1990s and 2009 but had not been confined to concentration camps.