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David Albright, president of the Institute for Science and International Security, a Washington-based think tank that has closely followed the North Korean nuclear issue, made the estimate based on recent developments to the despotic nation’s nuclear program. North Korea is believed to have 33 kilograms of separated plutonium and 175-645 kilograms of weapons-grade uranium, enough for between 13 and 30 nuclear weapons.

But according to the estimate, the materials are also enough for a further 12 weapons, using a “composite core” of plutonium and weapons-grade uranium. Mr Albright said the calculation took into account recent developments, including a reduction in Kim Jong-un’s plutonium stockpile due to two nuclear tests in 2016, and an addition of between 5.5 to 8 kilograms of plutonium from North Korea’s reprocessing campaign last year. He added: “Continued underground testing will provide North Korea opportunities to significantly improve its weapons in terms of less fissile material (particularly plutonium) per weapon, increased warhead miniaturisation, and greater explosive yields.”

GETTY Mr Albright said North Korea had enough material last year for up to 30 warheads

North Korea is expected to conduct a nuclear missiles test this weekend nuclear weapons north korea

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The expert also warned that North Korea aims to develop thermonuclear weapons, which allows weapons developers to create more warheads with less material. Mr Albright added: "It appears capable of developing thermonuclear weapons. “It is far more likely to be working on one-stage thermonuclear weapons rather than traditional two stage thermonuclear weapons, or 'H-Bombs’.

GETTY Kim Jong-un's army is also believed to be aiming to develop thermonuclear weapons

Photos from North Korea during celebration of the birth of late leader Kim Il Sung Wed, April 19, 2017 Covering a North Korean military parade is an emotional roller coaster, a visual and sensory barrage of socialist-realist propaganda Play slideshow AFP/Getty Images 1 of 23 North Korean leader Kim Jong-Un (R) attending a military parade in Pyongyang marking the 105th anniversary of the birth of late North Korean leader Kim Il-Sung

“Its existing knowledge should allow it to continue to make progress on a variety of deliverable nuclear weapons, even in the absence of additional underground nuclear tests." By 2020, North Korea will have enough fissile material for 25 to 50 nuclear weapons, but could extend to 60 should the country’s light water reactor go into operation. The alarming estimate comes as tensions between the totalitarian nation, China and the US begin to bubble over.

GETTY Donald Trump sent a Navy "armada" to the Korean Peninsula this week