US, Japan and South Korea vow tough response to N Korea H-bomb test

The US, Japan and South Korea have decided to launch a united and strong international response to North Korea's claim of a successful hydrogen bomb test.

US President Barack Obama made separate phone calls to his South Korean counterpart Park Geun-Hye and Japanese Prime Minister Shinzo Abe to discuss with them security situation in the region following North Korea's test.

"All the three leaders reiterated their pledge to forge a united and strong international response to North Korea's latest reckless behaviour," the White House said.

"Obama reaffirmed the unshakeable US commitment to the security of Japan, and the two leaders agreed to work together to forge a united and strong international response to North Korea's latest reckless behaviour," the White House said after Obama's phone call to Abe.

During the phone call between Obama and Park, the two leaders condemned the test and agreed that North Korea's actions constitute yet another violation of its obligations and commitments under international law, including several UN Security Council resolutions.

Secretary of State John Kerry also reached out to his Japanese and South Korean counterparts to discuss with them the North Korean nuclear test.

In his phone call to Japanese Foreign Minister Kishida, Kerry reiterated the steadfast commitment of the US to the security of Japan and emphasised the importance of a unified international response to the South Korean provocative actions.

"He also emphasised the importance of continued close bilateral cooperation with Japan and trilateral coordination with the Republic of Korea," State Department spokesman John Kirby said.

In his phone call to South Korean Foreign Minister Yun, Kerry reiterated the steadfast commitment of the US to the security of South Korea and emphasised the need for a unified international response to North Korea's provocative actions, Kirby said.

Meanwhile, former Deputy Secretary of State Nick Burns said the US and Asian countries should pressure the government of China to act much more resolutely to restrain and contain the North Korean regime.