A photo of the Oh family from 1991, the only known image taken inside North Korean prison camp Yodok [Amnesty]

Amnesty International says new satellite images and testimony from a former inmate show North Korea is holding about 200,000 people in its huge network of political prison camps where torture is rampant and conditions near slavery.

The human rights group based in London released on Wednesday recent satellite photos which show four of six camps located in the impoverished country's South Pyongan, South Hamkyung and North Hamkyung provinces.

North Korea has long been regarded as having one of the world's worst human rights records, but it rejects outside criticism and denies the existence of prison camps.

"North Korea can no longer deny the undeniable," Sam Zarifi, Amnesty International Asia Pacific director, said in a statement.

"Hundreds of thousands of people exist with virtually no rights, treated essentially as slaves, in some of the worst circumstances we’ve documented in the last 50 years," Zarifi said.

"Conditions in these camps are inhuman and [leader] Kim Jong-il must close them immediately," he added.

'Torture cells'

Prison camps are believed to have been in operation since the 1950s and can be categorised into two: 'total control zones' where inmates are never released without any proper trials; and 'revolutionary zones' where conditions are more lenient, Zarifi said.

"These are places out of sight of the rest of the world, where almost the entire range of human rights protections that international law has tried to set up for last 60 years are ignored," he said.

Kyoung-il Jeong, a former inmate at a revolutionary-zone Yodok prison, testified that inmates are fed 200 grams of corn gruel and often thrown into a cube "torture cell" where it is impossible to either stand or lie down.

"Seeing people die happened frequently – every day." Jeong said. "When an officer told me to, I gathered some people and buried the bodies. After receiving extra food for the job, we felt glad rather than feeling sad."

According to another testimony by a former detainee at Yodok, an estimated 40 per cent of inmates died from malnutrition between 1999 and 2001, Amnesty said.

A former inmate, Kim, testified that prisoners witnessed executions and those caught for attempting escape were executed after months-long interrogation.