Prime Minister Shinzo Abe on Friday questioned Pyongyang's claim that it tested a hydrogen bomb, noting that the blast appeared to be too small.
"It is hard to assume that it conducted a conventional hydrogen bomb test, considering the size of its seismic impact," Abe said during a session of the Lower House Budget Committee.
But he also said Pyongyang could have reduced the scale of the explosion on purpose because Wednesday's event was only a test.