The report said the institute recently succeeded in making "a more developed nuke" and Kim watched an H-bomb to be loaded into new ICBM.
The US Geological Survey recorded a 6.3 magnitude natural disaster at a depth of 0.0 km, a strong indicator the event may have been a nuclear test conducted by Kim Jong Un's military.
North Korea conducted two nuclear tests last year, the last almost a year ago, on the 9 September anniversary of the nation's founding.
Prime Minister Shinzo Abe was quick to express condemnation.
North Korea also tested a nuclear weapon in January of that year.
Experts estimate today's nuclear explosion produced a yield stronger than 100 kilotons, which, if correct, would dwarf the rogue nation's last nuclear test of around 20 kilotons in September past year.
"Every country with five nuclear explosions was well on its way to thermonuclear weapons by the fifth test", Lewis added.More news: Seahawks trade WR Jermaine Kearse for Sheldon Richardson
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The developments are raising already high tensions on the Korean Peninsula and in Washington that the North is getting closer to its goal of an arsenal of intercontinental ballistic missiles (ICBMs) that can reach the USA mainland.
North Korea is thought to have a handful of rudimentary nuclear bombs and has spent decades trying to flawless a multistage, long-range missile to eventually carry smaller versions of those bombs.
It has since tested two intercontinental ballistic missiles in July and last month, fired a potentially nuclear-capable missile over northern Japan. It urged North Korea to "stop taking erroneous actions that deteriorate the situation".
The U.S. Geological Survey called the first quake an explosion with a magnitude 6.3.
South Korea's weather agency says an apparent nuclear test by North Korea appears to have been several times stronger than its previous test.
The developments come amid high tensions over the North Korean missile and nuclear programs.
Tensions between North Korea and the global community flared against last week after Pyongyang flew a missile over Japan.