Japanese experts on nuclear and North Korean issues showed mixed views Wednesday over whether Pyongyang succeeded in testing a hydrogen bomb as it claimed, citing seismic data detected around the time of the test and other reasons.

Tatsujiro Suzuki, head of Nagasaki University's Research Center for Nuclear Weapons Abolition, said Pyongyang may not have gone as far as detonating a hydrogen bomb, but possibly tested a "boosted" fission bomb that is made by adding hydrogen isotopes to an atomic bomb.

"If it was a hydrogen bomb, the size of the earthquake (detected around the time of the purported nuclear test in North Korea) should have been larger," Suzuki said.