In the remote north-eastern corner of North Korea, close to the border of Russia and China, is Haengyong. Hidden away in the mountains, this remote town is home to Camp 22 - North Korea's largest concentration camp, where thousands of men, women and children accused of political crimes are held. Now, it is claimed, it is also where thousands die each year and where prison guards stamp on the necks of babies born to prisoners to kill them.
Over the past year harrowing first-hand testimonies from North Korean defectors have detailed execution and torture, and now chilling evidence has emerged that the walls of Camp 22 hide an even more evil secret: gas chambers where horrific chemical experiments are conducted on human beings.
Witnesses have described watching entire families being put in glass chambers and gassed. They are left to an agonising death while scientists take notes. The allegations offer the most shocking glimpse so far of Kim Jong-il's North Korean regime.
Kwon Hyuk, who has changed his name, was the former military attaché at the North Korean Embassy in Beijing. He was also the chief of management at Camp 22. In the BBC's This World documentary, to be broadcast tonight, Hyuk claims he now wants the world to know what is happening.
'I witnessed a whole family being tested on suffocating gas and dying in the gas chamber,' he said. 'The parents, son and and a daughter. The parents were vomiting and dying, but till the very last moment they tried to save kids by doing mouth-to-mouth breathing.'
Hyuk has drawn detailed diagrams of the gas chamber he saw. He said: 'The glass chamber is sealed airtight. It is 3.5 metres wide, 3m long and 2.2m high_ [There] is the injection tube going through the unit. Normally, a family sticks together and individual prisoners stand separately around the corners. Scientists observe the entire process from above, through the glass.'