North Korea says it has successfully carried out a hydrogen bomb test, which if confirmed, will be a first for the reclusive regime and a significant advancement for its military ambitions.

A hydrogen bomb is more powerful than plutonium weapons, which is what North Korea used in its three previous underground nuclear tests.

"If there's no invasion on our sovereignty we will not use nuclear weapon," the North Korean state news agency said. "This H-bomb test brings us to a higher level of nuclear power."

A senior U.S. administration official said it could take days to obtain the scientific data to determine whether this was a successful test. South Korea said it found it difficult to believe North Korea could test a hydrogen bomb, but hastily convened an emergency meeting.

The United Nations Security Council also will hold a meeting later Wednesday, at the behest of the United States and Japan.