Condemning North Korea’s surprise nuclear test, US Defence Secretary Ashton Carter and his South Korean counterpart today said Pyongyang’s provocations "should have consequences" as such a move is a threat to regional peace and stability.

Carter spoke over phone with his South Korean counterpart Han Min-koo to discuss potential alliance responses to North Korea carrying out the hydrogen bomb test.

"Carter and Han agreed that any such test would be an unacceptable and irresponsible provocation and is both a flagrant violation of international law and a threat to the peace and stability of the Korean peninsula and the entire Asia-Pacific region," the Pentagon Press Secretary, Peter Cook, said.

During the call, Carter reaffirmed the ironclad commitment of the US to the South Korean defence, and that this commitment includes all aspects of America’s extended deterrence, he said.

Han emphasized the strength of the US-South Korean alliance and its vital role in assuring peace and stability on the Korean Peninsula and across the Asia-Pacific.

"Carter and Han agreed that North Korea’s provocations should have consequences," Cook said.

The two defence leaders reaffirmed that the international community does not and will not accept North Korea as a nuclear state, and pledged that both sides would coordinate appropriate alliance responses to these provocations, Cook said.

They also agreed to the importance of close coordination with the international community and regional partners in condemning this action.

Prior to the call, Carter received a situational update from Gen Curtis Scaparrotti, commander, US Forces Korea.