Tetsuo Sawada, Assistant Professor at Tokyo Institute of Technology, believes the rapidly increasing strength of North Korea’s nuclear tests means developments can continue without more detonations.
And after 200 people were reportedly killed in a tunnel collapse at Kim Jong-un's mountain test site, North Korea is currently one nuclear experiment site down.
Mr Sawada told Russian news agency TASS: "North Korea is constantly upgrading its technology and has now reached a level where, in my estimation, it no longer needs to carry out nuclear detonations to test and develop the relevant weapons.
“Of course, this is my assumption, but it is based on the analysis of six tests conducted in that country.Related articles
GETTYNorth Korea's nuclear capability is believed to have reached a stage where tests aren't essential
"I believe the last test, the sixth one, was particularly successful. Authoritative experts estimate its power at 250 kilotonnes of TNT equivalent.
“North Korean official reports saying that was a hydrogen charge test are trustworthy, since the explosion of a conventional nuclear bomb cannot be so powerful.
“A qualitative development of North Korea’s nuclear program is evident, and, apparently, it will continue to push ahead with its efforts to upgrade its potential by creating more compact and light charges."
Mr Sawada used India and Pakistan, both themselves nuclear powers, as historical examples for evidence behind his claim that Pyongyang no longer needs to conduct nuclear tests.
Both countries conducted a series of detonations in May 1998 but no tests have since been recorded.
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North Korean leader Kim Jong Un provides guidance on a nuclear