North Korea's latest nuclear test is "extremely regrettable" and violates the international community's repeated demands, the head of the UN atomic watchdog said Sunday.

"Today's nuclear test by the Democratic People's Republic of Korea (DPRK) is an extremely regrettable act," International Atomic Energy Agency head Yukiya Amano said in a statement.

"This new test, which follows the two tests last year and is the sixth since 2006, is in complete disregard of the repeated demands of the international community," Amano said.

Read More: NKorea declares H-bomb test 'a perfect success'

UN Security Council resolutions have reaffirmed that Pyongyang should not conduct any further nuclear tests and abandon all nuclear weapons and existing nuclear programmes, Amano added.

Amano said that the Vienna-based IAEA, whose inspectors were kicked out of North Korea in 2009, "remains ready" to contribute to a peaceful resolution of the situation.

The test was North Korea's sixth and far more powerful than any weapon it has previously detonated.

Pyongyang declared the test of what it called a hydrogen bomb to be a "perfect success".