Prisons house convicts, who are subjected to forced labor, but the worst human rights abuses occur in political prison camps.

Detention centers are similar to police holding cells, but holding facilities and indoctrination camps are clandestine operations that have been used to hold repatriated defectors without trial since the early years of the millennium.

Based on testimony of about 13,000 North Korean defectors, North Korean Human Rights Archives said the regime operates 210 detention centers and 210 labor camps, 23 prisons, 5 indoctrination camps, 27 holding facilities, and 6 political prison camps including in Yodok, Pukchang and Hoeryong.

At least 480 prisons and detention facilities are scattered around North Korea, an NGO claimed Tuesday.

A defector who was detained at a prison in Hamhung in the late 1990s said security forces "took about 500 people to a barren wilderness, where they threw shovels at them and told them to dig tunnels to live. Many died later."

Almost no detention facilities provide inmates with foods, but they eke out a meager existence by tending vegetable gardens. In some facilities, guards turned livestock sheds into detention cells.

"They built walls around pigsties and used them as holding pens," said another defector who was held in a camp in the late 2000s. "More than 100 inmates were put into a cell that can accommodate only about 30."

The State Security Department routinely used violence in interrogations. A female defector testified, "I was raped by a guard at a holding center, and was forced to have an abortion later."

The regime has either hidden the concentration camps from the outside world or given out false information about them, NKHRA said. It officially admitted the existence of only three of the 23 prisons, using Sariwon Prison in North Hwanghae Province and Chonnae Prison in Gangwon Province as display showcases.

"The North is operating numerous detention facilities across the country," said Yoon Yeo-sang of NKHRA. "It seems the regime significantly increased the number of facilities to tighten controls on the people when the economic situation worsened after the 1990s."