Satellite images released by the rights group, Amnesty International, show on-going developments at North Korea's main political prison camps - camp 15 and 16.

The images, released on Thursday, of the camps known as Kwanliso were taken in May 2013 and show new housing blocks and expansion of production facilities.

Mr Lee, a former prison official of camp 16 described the conditions at the prison camps as "degrading." 

"The purpose of prison camps is to oppress, degrade, and violate the inmates for as long as they are alive," Lee told Amnesty.

"The prisoners are only humans insofar as they can speak. In reality though, they are worse off than animals." he added.

Thousands languishing

Calling on the North Korean government to release all political prisoners, Amnesty's Rajiv Narayan, said, "The conditions in these camps are very severe.

"Not only do they have to work pretty much most of the day in dangerous conditions where they could die at any time, they also have very little food.

"So they could die of malnutrition, but also we’ve heard that torture is rampant, that there is rape of women inmates and of course executions as well."

It is estimated thousands of political prisoners languish in jails in North Korea, which has the biggest standing army in the world.

Source: Al Jazeera