Kim Jong-un Says North Korea Has an H-Bomb — But No One Believes Him

North Korea's leader Kim Jong-un made a rare appearance on Thursday to claim his country has successfully developed a hydrogen bomb — but outside experts were skeptical.

Kim made the comments as he toured the Phyongchon Revolutionary Site, which is dedicated to his father Kim Jung-il, and grandfather, Kim Il-sung, the official KCNA news agency said.

The work of Il-sung "turned the DPRK [Democratic People's Republic of Korea, North Korea's official name] into a powerful nuclear weapons state ready to detonate a self-reliant A-bomb and H-bomb to reliably defend its sovereignty and the dignity of the nation," KCNA quoted Jong-un as saying.

A hydrogen bomb, also known as a thermonuclear bomb, uses more advanced technology to produce a significantly more powerful blast than an atomic attack.

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But pretty much no one outside the hermit kingdom was convinced that North Korea had actually acquired the technology. An official at South Korea's intelligence agency told Yonhap news agency there was no evidence that the North had hydrogen bomb capacity, and believed Kim was speaking rhetorically.

North Korea conducted a series of underground nuclear tests in 2006, 2009, and 2013, which prompted the United Nation's Security Council to impose sanctions on the country banning trade and financing activities that aid its weapons program.

Despite the underground tests, outside experts suspect the North is short of achieving the capability to put a nuclear warhead on a missile, although it has boasted it had succeeded in the miniaturization of a weapon.

If the hydrogen bomb claim is true, it would indicate advances in the North's pursuit of nuclear weapons.

"I think it's unlikely that they have an H-bomb at the moment, but I don't expect them to keep testing basic devices indefinitely, either," said Jeffrey Lewis of the California-based Middlebury Institute of International Studies at Monterey.

It was possible the North was referring to the technology of boosting the yield of a nuclear device, possibly using fusion fuel, Lewis said. North Korea claimed in 2010 that it had successfully developed fusion technology.

Assessing progress of the North's nuclear program is difficult because no one outside a close circle of leaders and experts knows what advances have been made.

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The Foreign Ministry in China, North Korea's most important economic and diplomatic backer, said China was dedicated to ensuring the denuclearization of the Korean peninsula and resolving problems through talks.

"We hope that all sides can do more to ameliorate the situation and make constructive efforts to maintain peace and stability on the peninsula," ministry spokeswoman Hua Chunying told a daily news briefing when asked about Kim's remarks.

Impoverished North Korea and rich, democratic South Korea remain technically at war after their 1950-53 conflict ended in a truce, not a treaty. The North has threatened to destroy the South and its major ally, the United States, in a sea of flames.

Watch the VICE News documentary, Launching Balloons into North Korea: Propaganda Over Pyongyang: