Scientists have cast doubt on North Korea's claims they have detonated a hydrogen bomb, arguing seismic pattern produced by the blast was too similar to previous nuclear tests.
The secretive state claimed to have successfully conducted the explosion as a result of the "indigenous wisdom, technology and efforts the DPRK".
Despite no formal confirmation, The EU and Nato were quick to condemn North Korea over their hydrogen bomb claims, with UN United Nations Secretary-General Ban Ki-moon describing the allegations as "deeply troubling".
If confirmed, it would be a huge leap forward for North Korea, who have successfully been carrying out nuclear tests for atomic bombs since 2006.
However, there are already doubts regarding the claims from North Korea, with Foreign Secretary Philip Hammond and US House Speaker Paul Ryan dismissing the boasts as nothing more than "provocation" and Japanese monitoring posts also saying they have not detected any radiation being emitting from North Korea's alleged test site.
Experts have now suggested the amount of energy, or yield, from the explosion appears to be too small to be considered to be from a Hydrogen bomb.
Following the blast, The US Geological Survey measured an earthquake with a magnitude of 5.1, with the Comprehensive Test Ban Treaty Organization (CTBTO) recording it as equivalent to a 4.9, both of which fall way short of what would happen had a hydrogen bomb went off.
Reading of seismic activity also suggests most recent blast is too similar to ones carried out by the country in 2006, 2009 and 2013.
The New York Times reports that Lee Cheol-woo, a member of the intelligence committee of the South Korean National Assembly, estimated the explosive yield that was equivalent to six kilotons of TNT compared to the "hundreds of kilotons or, even if it is a failed test, tens of kilotons" of an hydrogen bomb.
Bruce Bennett, an analyst with the Rand Corporation, told the BBC: "The bang they should have gotten would have been 10 times greater than what they're claiming. So Kim Jong-un is either lying, saying they did a hydrogen test when they didn't, they just used a little bit more efficient fission weapon – or the hydrogen part of the test really didn't work very well, or the fission part didn't work very well."
Chemical weapons analyst Karl Dewey, of IHS Jane's, believes the blast may have been caused by a boosted fissure weapon such as a less-powerful atomic bomb.
He said: "Hydrogen bombs use lithium deuteride and it is not known if North Korea has the infrastructure to create such material. What may be more plausible is the development of what is known as a boosted fission weapon. Simple fission weapons or boosted weapons can be used to set off a thermonuclear secondary, but shouldn't be confused with them."