North Korea's latest nuclear test could have involved a boosted fission weapon or simply a conventional nuclear bomb, and the communist nation might have exaggerated the test for political and other purposes, a congressional report said.

The Congressional Research Service made the assessment in a report issued earlier this month, pointing out experts' views that the yield of the Jan. 6 test was too low to believe it involved a hydrogen bomb as claimed by Pyongyang.

"Another possibility discussed by technical experts is that the January 6 test was a 'boosted' fission weapon. Generally, countries would test a boosted fission weapon as the next step after testing fission weapons, on the path to developing a hydrogen bomb," the CRS report said.

A boosted fission weapon is also "lighter in weight and smaller in size and may explain the North's claim that they have tested a 'mini H-bomb,'" the report said, adding that in order to be delivered on longer-range ballistic missiles, nuclear warheads need to be of a lower weight and size than the most simple nuclear fission bomb design would allow.

"It is also possible that the device was a fission bomb, but that the North Korean government claimed it was a hydrogen bomb for other purposes such as domestic political support, deterrence impact on its neighbors, or possibly an exaggerated claim by scientists to the leadership," the report said.

Following Pyongyang's H-bomb claims, the White House expressed strong skepticism, saying "initial analysis is not consistent" with the North's claims. U.S. nuclear experts have expressed doubts, saying its yield was too low to believe that such an advanced bomb, way more powerful than conventional nuclear weapons, had been detonated.

The latest test marked the North's fourth nuclear test following previous ones in 2006, 2009 and 2013. (Yonhap)