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.

“We need to conduct further analysis,” Abe said.

Earlier the day, Defense Minister Gen Nakatani said the blast registered as a magnitude-5.0 earthquake, which is comparable to Pyongyang’s past three nuclear tests.

The Obama administration said it believes a nuclear blast took place, but on Thursday cast increasing doubt on the claim that it was a hydrogen bomb.

“Our analysis . . . indicates that it’s not consistent with the North Korean claims of a hydrogen bomb test,” Pentagon press secretary Peter Cook told reporters in Washington. “We’re continuing to receive information and analysis, and we’ll over the coming days we hope receive even more information that might give us a better understanding of exactly what took place there.”

On Wednesday, the White House said it has not revised its assessment of North Korea’s military capabilities.

Hydrogen bombs release about 1,000 times the energy of a standard atomic bomb, according to Tatsujiro Suzuki, a professor at Nagasaki University’s Research Center for Nuclear Weapons Abolition. They are also significantly harder to make.

South Korea’s Yonhap news agency said the seismic magnitudes of the North’s past tests were 3.7 in 2006, 4.5 in 2009 and 4.9 in 2013.

Some analysts said Pyongyang might have juiced the blast by adding tritium, a radioactive form of hydrogen. A weapon of this type is more advanced than a conventional atomic bomb but far less powerful than an H-bomb.

Meanwhile, Nakatani claimed there is a chance that Pyongyang, faced again with global condemnation, might take more “provocative actions” — including a ballistic missile test.

On Friday, South Korea retaliated by resuming propaganda broadcasts along the heavily fortified demilitarized zone with North Korea.

This might heighten tensions between the two Koreas, and Tokyo will monitor the situation “with grave concern,” Nakatani said.

In a related move the same day, lawmakers in both houses of the Diet adopted resolutions condemning North Korea for the nuclear blast.

Pyongyang “forcibly conducted” the test while “ignoring” the voice of international society, the resolutions said. The Upper House resolution called on the United Nations Security Council to adopt a resolution and tack on more sanctions against the North.

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