GETTY•REUTERS North Korean leader Kim Jong Un was the victim of an apparent assassination attempt

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Increased activity at an atomic plant has sparked fears that the secretive communist state is gearing up for further trials involving its nuclear arsenal. A monitoring group in the US said images taken of Punggye-ri on North Korea's east coast showed construction of a test tunnel at a site that has been used for three underground nuclear tests since 2006. Rumours have also circulated that the North Korean leader narrowly avoided death after explosives were found at an airport he was due to visit.

A stack of explosives was reportedly found hidden inside the roof of Kalma Airport on October 6 - a day before Jong-Un was scheduled to arrive. The TNT was discovered by North Korea's State Security Department (SSD) just hours before the visit as the device had been missed during an earlier sweep of the airport by Jong Un's personal Supreme Guard Command bodyguards.

AP What appears to be a new tunnel under mountains where North Korea conducts nuclear test explosions

GETTY Military parade in Pyongyang earlier this year

A source told Radio Free Asia: "Kim Jong Un's visit to Kalma airport was cancelled immediately, as explosives were found a day before his visit. "The explosives were planted inside the roof of the airport's information desk. "The explosive found at the desk was a box of TNT which North Koreans use to blast through mines. "A box can hold about 100 explosives and each [explosive] would weigh around 200g."

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Fresh nuclear testing could be seen as one way to appease the tyrant's military aides. The isolated nation has been steadily working on its nuclear programme for years although a fourth test is not seen as imminent. Jeffrey Lewis, author of the nuclear testing report by 38 North, a North Korea project at Johns Hopkins University in Washington, said another test would "depend on political factors" rather than technical or military ones.

GETTY Kim Jong-Un (C) attending the 4th Conference of Korean People's Army (KPA) Artillery Personnel

GETTY The North Korean despot was at the talks over the weekend in Pyongyang

REUTERS Kim Jong Un provides field guidance to Tree Nursery No. 122 of the Korean People's Army

North Korea has conducted three underground nuclear tests since 2006. The last, in 2013, drew international condemnation including from China, its main diplomatic ally. Lassina Zerbo, head of the Comprehensive Nuclear-Test-Ban Treaty Organisation, claimed the construction work picked up by satellite imagery was likely to be a PR stunt: "I'm tempted to believe that the fourth tunnel is just a bluff to put pressure on the international community to resume discussion with them. "One would not anticipate that North Korea would go for new testing at a time when they are engaged in discussions with their brothers from the South. "In the 21st century, they are the only country to have conducted a nuclear test explosion. In the 21st century, the world is too civilised for anyone to resume testing".

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