North Korea said it successfully tested a miniaturized hydrogen nuclear device on Wednesday, claiming a significant advance in its strike capability and setting off alarm bells in Japan and South Korea.
The test, the fourth time the isolated state has exploded a nuclear device, was ordered by young leader Kim Jong Un and successfully conducted at 10 a.m. local time North Korea's official KCNA news agency said.
"Let the world look up to the strong, self-reliant nuclear-armed state," Kim wrote in what North Korean state TV displayed as a handwritten note.
The nuclear test drew condemnation abroad, with China, the North's chief ally, expressing "resolute opposition" and saying it would lodge a protest with Pyongyang.
While a fourth nuclear test had been long expected, the claim that it was a hydrogen device, much more powerful than an atomic bomb, came as a surprise, as did the timing. It ensures that North Korea will be a key topic during the U.S. presidential campaign.
North Korea has long coveted diplomatic recognition from Washington but sees its nuclear deterrent as crucial to ensuring the survival of its third-generation dictatorship.
"With Iran being off the table, the North Koreans have placed themselves at the top of the foreign policy agenda as far as nation-states who present a threat to the U.S.," said Michael Madden, an expert on the country's secretive leadership.
South Korean intelligence officials and several analysts however questioned whether Wednesday's explosion was indeed a full-fledged test of a hydrogen device.
The device had a yield of about 6 kilotons, according to the office of a South Korean lawmaker on the parliamentary intelligence committee – roughly the same size as the North's last test, which was equivalent to 6-7 kilotons of TNT.
"Given the scale, it is hard to believe this is a real hydrogen bomb," said Yang Uk, a senior research fellow at the Korea Defence and Security Forum.
"They could have tested some middle stage kind [of device] between an A-bomb and H-bomb, but unless they come up with any clear evidence, it is difficult to trust their claim."