A senior UN official told ABC News that the U.S. and Japan have called for an emergency meeting of the United National Security Council after North Korea claimed to have successfully tested a hydrogen bomb.

A magnitude 5.1 earthquake was measured in the country near the site of an earlier nuclear weapons test was felt before the announcement. The trembler was detected about 12 miles ENE of Sungjubaegam and the South Korean weather agency said indications were that it was 'artificial.'

'We have perfectly succeeded in testing our first hydrogen bomb,' an anchor said on North Korean state TV. 'It was one hundred percent capable from our own wisdom, technology, and power. We have now scientifically test-proved a miniaturized hydrogen bomb.'

The anchor added that 'If there's no invasion on our sovereignty we will not use nuclear weapon, this H-bomb test brings us to a higher level of nuclear power.'

The test took place at 10 a.m. local time, the regime said in a televised statement.

'U.S. Forces Korea is aware of reports on North Korea's nuclear test today,' a U.S. Pacific Command spokesman said. 'We remain vigilant and are fully committed to working closely with our Republic of Korea ally to maintain security on the peninsula.'

A hydrogen bomb is hundreds of times more powerful than the atomic bomb that devastated Hiroshima in 1945.

The North Koreans have signaled for some time the test was a possibility, said Mike Chinoy, with the U.S.-China Institute at the University of Southern California.

'Kim Jong Un made public statement a few weeks ago saying that (the country was) developing a hydrogen bomb.'

But, said Bruce Bennett, North Korea's claims ought to be taken with a grain of salt. Bennett is a senior defense analyst at the nonprofit, nonpartisan Rand Corp.

'North Korea appears to have had a difficult time mastering even the basics of a fission weapon, this suggests that unless North Korea has had help from outside experts, it is unlikely that it has really achieved a hydrogen/fusion bomb since its last nuclear test, just short of three years ago.'