The United States urged North Korea on Thursday to completely give up all of its nuclear weapons and programs after leader Kim Jong-un claimed the communist nation developed hydrogen bombs considered more powerful than conventional atomic weapons.

During a visit to a historic site for the North's arms industry, Kim said the country has 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."

It was believed to be the first time that Kim has publicly mentioned the North's development of an H-bomb.

"We are aware of North Korean state media reports on Kim Jong-un's claims regarding development of nuclear weapons, including hydrogen bombs," State Department spokeswoman Katina Adams said, adding that she cannot comment on intelligence matters.

"We continue to call on North Korea to comply with its international commitments and obligations," she said. "North Korea must abandon all nuclear weapons and existing nuclear programs in a complete, verifiable and irreversible manner, and cease all related activities immediately."

The spokeswoman said the international community "stands united in its firm opposition" to the North's development of nuclear weapons and Pyongyang will not achieve the "prosperity and security it seeks and will remain isolated until it abandons its illicit weapons programs and abides by its international obligations and commitments."

South Korea's intelligence community was skeptical about the North's H-bomb capability, with an intelligence official saying that the North is not believed to have such capabilities when it has not yet mastered the technology to miniaturize nuclear warheads.

In Beijing, China said it is aware of the North's H-bomb claim, and called for all relevant countries to make greater efforts to denuclearize the Korean Peninsula, lower tensions and maintain peace and stability.

North Korea has conducted three underground nuclear tests so far, in 2006, 2009 and 2013. The country has also conducted a series of long-range missile or rocket launches since 1998. In its most recent launch in late 2012, the North succeeded in putting a satellite into orbit.

Analysts have warned that it is only a matter of time until the North develops nuclear-tipped missiles. Some experts have recently warned that the communist nation's nuclear arsenal could expand to as many as 100 bombs by 2020.

The six-party talks aimed at resolving the North Korean standoff have been stalled since late 2008. North Korea demands the unconditional resumption of negotiations, while the U.S. says that Pyongyang must first take concrete steps demonstrating its denuclearization commitments. (Yonhap)