Announcing the results of the United States’ analysis, US National Intelligence Director John Negroponte confirmed that scientists had detected “radioactive debris” from samples taken last Wednesday, two days after the North Korean test.

He added that the detonation had been slightly less than one kiloton – far short of the 15 kilotons that wiped out Hiroshima or the 21 kiloton device that was dropped on Nagasaki – but enough, said analysts, to establish that North Korea is at least on the right track toward developing a nuclear arsenal and becoming the eighth member of the so-called nuclear club, or those countries that possess nuclear weapons capabilities.

US officials have also said they have intelligence that North Korea could be planning another, and perhaps stronger, test in the near future, US media reported.

The confirmation of the test’s authenticity was immediately greeted by sanctions from the United Nations (UN) Security Council, which convened in emergency session yesterday.

Until yesterday, details of the blast had been sketchy at best, with most of the information about it coming from the state-controlled Korea Central News Agency (KCNA) and conflicting seismic data from monitoring stations around the world.

In the hours following the explosion, atmospheric tests registered no unusual spikes in radioactivity, which is typical, according to scientists, as an underground nuclear blast can take as long as two weeks to detect.

But it is now clear from monitoring conducted by the United States and Russia, which shares a sliver of border with North Korea, that the test took place in the remote P’unggye region.

US security analyst spent the seven days since the explosion poring over air samples, seismic readings, satellite imagery and communications intercepts in an effort to reach a conclusion on the nature of the test, world news agencies reported.

The finding comes at a diplomatically sensitive time, and puts China – one of the Security Council’s permanent members with veto power – in the diplomatic hot seat. As North Korea’s closest ally on the five-country council – whose permanent members also include the United States, Russia, France, and the United Kingdom – China’s backing of sanctions was earlier in question.

Nicholas Burns, US undersecretary of state for political affairs, said there would be "enormous pressure on China to live up to their responsibility" in enforcing the sanction, according to the London Guardian.

But Beijing is expected to do its part, and has instituted new inspections by Chinese officials of trucks bound for North Korea to punish its reclusive ally for its nuclear programme, the Guardian reported.

Japan and Australia, meanwhile, have announced that they may take measures beyond the new UN resolution, which could include stop-and-search missions against North Korea ships, international news agencies reported. The US-sponsored resolution demands North Korea eliminate nuclear weapons but rules out military action against the country, as the Russians and Chinese demanded.

Following the resolution’s unanimous passage, North Korea’s ambassador to the UN accused the Security Council of a "gangster-like" move that neglected the nuclear threat posed by the United States, the Guardian said.

Russia’s foreign ministry said yesterday that it wanted an "adequate response" from the North Korean leadership to the resolution. Its statement confirmed the unusual show of regional unity against North Korea, the paper said.