Features spotted on satellite images by a researcher in America are thought to offer clues about the huge size of an underground factory in North Korea.
Open source researcher Jacob Bogle used the images to try and glean information about the country's secretive Kanggye General Tractor Plant, which is located to the north of the country in Chagang province.
Up to 20,000 people are believed to be employed by the plant and Bogle sought to determine the scale of the underground building by analysing features such as ventilation shafts sticking out of the ground.
Reports indicate staff at the factory work to produce a range of arms for North Korea, including munitions, including anti-tank artillery and small arms ammunition.
"Outside, in front of the hill that houses the underground portion, there’s about 50 hectares of administrative buildings, warehouses and even a small stadium for employees to play football," Bogle explained.
He continued: "The factory is somewhat nondescript. But then all you have to do is look at the hill and you can see small buildings extending straight into the rock and at least nine entrance tunnels. In fact, it’s a little difficult getting an exact count of just how many tunnels there are."
Using his analysis, Bogle estimated the factory covers 176,000 square metres, which roughly equates to the size of 25 football pitches.
Bogle has previously collated and analysed imagery of other underground factories around North Korea and discovered most of them have up to three access tunnels. In comparison, the Kanggye General Tractor Plant appears to have at least nine access tunnels.
"So, to carry on with the Bond villainy analogy, you have this somewhat normal looking factory, surrounded by the region’s mountains," Bogle said. "But then you look more closely and there’s this hidden network of tunnels all producing weapons for one of the largest militaries in the world and that’s headed by a guy who murdered his own brother and uncle."
Bogle notes the plant includes recreational facilities like a stadium and a swimming pool, as well as a medical clinic and 'other amenities for the workers and their families'.
"Work at the factory is likely to be difficult," he speculated. "There would be no public discussion of injuries or safety failures, but there is no reason to believe that workers are any less safe than at other North Korean arms factories."
Images released by Korean Central News Agency, the state’s news agency, have previously offered insights to the plant, showing workers in a swimming pool and putting on performances in a sports hall during a visit by North Korea's leader Kim Jong Un.
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