North Korea is expanding its existing prison camps and "blurring the lines between the camps and the surrounding population", according to Amnesty International.
The organisation has collated satellite images which it says show extensive work on existing camps and the construction of perimeter fences, suggesting villages adjacent to some camps have been swallowed up within a wider zone.
"We expected to find a new prison camp," Frank Jannuzi, deputy executive director of Amnesty USA, said.
"What we found is in some ways even more worrisome. The creation of a security perimeter with controlled access points and guard towers beyond what appears to be the formal boundaries of Camp 14 blurs the line between more than 100,000 people who suffer in North Korea's Kwan-li-so system and the neighbouring civilian population."
Amnesty has released five images. The first shows an overview of the Ch'oma-Bong valley, 70km to the north-east of the capital Pyongyang.
According to the human rights organisation, a 20km perimeter fence has been built encircling the wider valley and joining it to the existing prison camp. Amnesty has marked the fence on the satellite image with a blue line for clarity.
"Analysts found that from 2006 to February 2013, North Korea constructed 20km of perimeter around the Ch'oma-Bong valley ... and its inhabitants, new controlled access points and a number of probable guard towers," the group said.
"Analysts also found construction of new buildings that appear to house workers, likely associated with an expansion of mining activity in the region."
A second image shows the same area but at a slightly different scale. At the south-west corner of the image is Camp 14, also known as the Kaechon internment camp.
Amnesty International has highlighted, in red, what it claims are 20 newly established "probable guard posts" which are dotted along the perimeter fence.
"The activity points to a tightening in the control of movement of the local population adjacent to Camp 14, thus muddying the line between those detained in the political prison camp and the valley's inhabitants," Amnesty said.
"This raises fears for the population within the perimeter the current conditions faced by them and the North Korean government's future intentions for the valley and those that live there."
Two more images show 'before and after' photographs of two specific areas of a camp. They both show significant building work.
The existence of North Korean prison and hard labour camps has been well documented over several decades.
The North Korean government, led by the young and unpredictable Kim Jong-Un, denies the existence of the camps. A request for an interview with North Korea’s Ambassador to the UK was declined.
In an email to Sky News, a spokesman at the country's embassy in London rejected all claims of the existence of prison camps and referred us to a 2012 statement from the North Korean government.
The 2012 statement read: "The DPRK flatly rejects and vehemently denounces the anti-DPRK 'human rights resolution' which the hostile forces adopted to bring down the Korean-style socialist system centered on the popular masses by abusing the noble idea of human rights, prompted by their sinister political purposes."
Conditions inside the prison camps are said to be horrific and testimony from the few who have escaped from the camps is shocking.
Former detainees describe "three generations of punishment". The person who committed the political 'crime' is locked up along with his or her entire family. The subsequent two generations of children are then born and also imprisoned in the camp.
Extreme torture is said to be widely used against the prisoners, who are forced to work on the land like slaves. As many as 200,000 North Koreans are said to be held in these camps with no prospect of release.
Kim Jong-Un, who is just 28 years old, has publicly stated that his first three priorities of government are to strengthen the military. He is, according to observers, entirely ignoring a growing number of his people who are suffering the effects of extreme poverty.
In December, North Korea successfully launched a satellite into orbit . In February, it tested an underground nuclear device. It has made no secret of its desire to combine these two developing technologies to create a nuclear weapon.
The nuclear test prompted international condemnation and a meeting of the United Nations Security Council which is expected to announce further sanctions on Pyongyang later today.
The influence of China remains key. Beijing is, historically, Pyongyang's only real ally. Through trade across the border the two countries share, China effectively props North Korea up.
Diplomatic sources in Beijing have told Sky News they are encouraged by the fact the latest resolution appears to have been drawn up together by the US and China, suggesting encouraging cooperation between Washington and Beijing.
The United Nations has been trying to gain access to the region for years. In November, the UN Special Rapporteur for North Korea, Marzuki Darusman, expressed his disappointment that North Korea's new leader had not allowed his team any access.
"Despite my repeated requests, I have not been granted access to the Democratic People's Republic of North Korea (DPRK)," he said.
"I regret that a fresh approach has not been forthcoming under new leadership of the DPRK.
"There is no sign of improvement of the human rights situation ... I continue to be concerned about the human rights and humanitarian situation in the country."