Obama accused the North of "directly and recklessly challenging the international community", blaming it for increasing tensions and undermining stability in northeast Asia.

"The danger posed by North Korea's threatening activities warrants action by the international community," Obama added.

In Beijing the Chinese government said it was "resolutely opposed" to North Korea's nuclear test, state media reported, citing a statement by the Chinese foreign ministry.

North Korea said Monday's underground test, more powerful than its atomic bomb test in 2006, was part of moves to strengthen its nuclear deterrent.

'Intolerable act'

The test was also expected to overshadow a meeting of European and Asian foreign ministers gathering in the Vietnamese capital, Hanoi, on Monday for two days of talks.

The test has sparked widespread condemnation and a call for global action [GALLO/GETTY]
Christina Gallach, spokesperson for Javier Solana, the European Union foreign policy chief, told Al Jazeera the EU was "very worried" over the test and would be seeking a united stance with Asia.

"We think that this is a complete challenge not just to the stability of the Asia Pacific region but also to the whole world," she said.

"We think the best manner to impose on the North Korean regime is total international condemnation."

Hirofumi Nakasone, the Japanese foreign minister, speaking in Hanoi, said Tokyo was particularly at risk, given its proximity to the North and its history as the only nation to suffer a nuclear attack.

"It is an act that we can never tolerate," Nakasone said after meeting Yu Myung-Hwan, his South Korean counterpart.

In a statement issued by its foreign ministry, France said it would consult the UN Security Council partners "on the consequences to draw from this serious act ... in particular on strengthening sanctions".

Emergency session

"[T]hey deserve and get nothing other than our absolute condemnation, and that condemnation should be echoed around our region and the globe"

Stephen Smith, Australian foreign minister

Russia, the current chair of the UN Security Council, convened an emergency meeting of the 15-member body later on Monday to discuss the issue, while Japan and South Korea formed crisis management teams.

The Interfax news agency quoted Sergei Lavrov, the Russian foreign minister, as saying that his country was "concerned" over the reported tests.

The nuclear test had a force of about 20 kilotonnes, the Itar-Tass news agency quoted a source in Russia's defence ministry as saying. A kilotonne is equivalent to 1,000 tonnes of TNT.

A senior official at the North Korean embassy in Moscow told the Itar-Tass that Pyongyang may carry out more nuclear tests unless the US ends its policies of "intimidation".

In Tokyo ministers scrambled to convene a national security meeting, including plans to consider tightening its own sanctions on the reclusive state.

Taro Aso, the Japanese prime minister, said the test was unacceptable and a violation of UN resolutions, adding that Japan would seek a new resolution condemning the act.

'Grave challenge'

North Korea's test came as a surprise to most in the region and around the world [Reuters]
South Korean military officials also held crisis talks in the capital Seoul while Lee Myung-Bak, the president, chaired a national security council meeting.

A spokesman for the president said Monday's test posed a "grave challenge" to international non-proliferation efforts, adding that South Korea will join six-party members to "ask the UN Security Council to take appropriate action".

Australia said North Korea's nuclear test was provocative.

"On the basis that North Korea has conducted a nuclear underground explosion, they deserve and get nothing other than our absolute condemnation, and that condemnation should be echoed around our region and the globe," Stephen Smith, the Australian foreign minister, told parliament.

The US, Japan, Russia and South Korea, along with China, have been involved in six-party talks with North Korea since 2003 which are aimed at putting an end to its nuclear programme.