World leaders went into diplomatic overdrive today after North Korea announced that it had carried out its first nuclear weapons test, despite repeated international warnings not to do so.
The blast occurred at 10.36am (0136GMT), apparently in a disused coalmine near the town of Kilju in the northeast of the country.
There was no official confirmation of the North Korean claim. Seismologists detected a tremor measuring around 3.6 after the blast, suggesting an explosive yield of as low as 500 tonnes of TNT, only one-thirtieth of the destructive power deployed against Hiroshima in 1945.
One US official told Reuters that it could take several days for intelligence analysts to determine whether the event was the result of an unsuccessful nuclear test, a small nuclear device or a non-nuclear explosion.
"In terms of yield, we have it registering at less than four on the Richter scale. That’s the kind of thing that could be the result of several hundred tons of TNT, rather than a nuclear test," the official said.
The Korea Central News Agency (KCNA), the official mouthpiece of the Stalinist regime, said that no radiation had escaped in the blast, which it hailed as "a great leap forward in the construction of a great, prosperous, powerful socialist nation".
"The nuclear test was conducted with indigenous wisdom and technology 100 per cent," KCNA added. "It marks a historic event as it greatly encouraged and pleased the KPA (Korean People’s Army) and people that have wished to have powerful self-reliant defence capability."
The test flew in the face of a warning from the UN Security Council and drew fierce condemnation from around the world, including from China - the closest that North Korea has to an ally. Beijing expressed its "resolute opposition" to the "brazen" test.
In a short statement at the White House, President Bush said: "Last night, the government of North Korea proclaimed to the world that it had conducted a nuclear test. We’re working to confirm North Korea’s claim.
"Nonetheless, such a claim itself constitutes a threat to international peace and security. The United States condemns this provocative act. Once again North Korea has defied the will of the international community, and the international community will respond.
Mr Bush said that he had discussed the crisis with the leaders of China, Russia, Japan and South Korea "and all of us agreed that the proclaimed actions taken by North Korea are unacceptable and deserve an immediate response by the United Nations Security Council".
Ambassadors from the 15 Security Council members were holding emergency talks at UN headquarters in New York today to discuss the crisis and adopt a resolution against Pyongyang.
First, however, the ambassadors met to approve the nomination of Ban Ki Moon, the South Korean Foreign Minister, to succeed Kofi Annan as UN Secretary-General - which John Bolton, the US Ambassador to the UN called an "appropriate juxtaposition" highlighting the gulf between North and South 61 years to the day after the division of Korea.
Mr Bolton said that Council members were hoping for "very swift action" on the crisis, adding: "We'll be going 24/7 if we need to be to get this resolution adopted by the Council."
Quite what action the UN can take against the North Koreans remains to be seen - as a country that has barely any international trade, it is virtually immune to economic sanctions.
But North Korea appears isolated as never before, given the reaction from China - the closest thing it has had to an ally.
The blast came the day after President Hu agreed to work with Shinzo Abe, the new Japanese Prime Minister, to work together to avert a North Korean nuclear test. After his visit to Beijing, Mr Abe arrived for a scheduled visit to Seoul only minutes after this morning's announcement from Pyongyang.
Details of the blast were sketchy. Sergei Ivanov, the Russian Defence Minister, estimated its yield at between five and 15 kilotons, or up to 15,000 tonnes of TNT, making it potentially as powerful as the bomb which devastated the Japanese city of Hiroshima in 1945.
But an Australian seismology institute put the figure at one kiloton and the Korea Institute of Geoscience and Mineral Resources, backed up by other experts, said that the size of the tremor suggested an explosive force equivalent to 550 tons of TNT - a surprisingly low explosive yield for a nuclear test.
"If it was a one-kiloton explosion, that would be disappointing small - a completely damp squib. It's very unlikely that they would have designed a bomb to have a yield as small as that," said James Acton, science and technology researcher at Vertic, a non-governmental organisation in the UK that works for nuclear non-proliferation.
The blast makes North Korea the eighth country in the world to openly carry out a nuclear test after the United States, Russia, Britain, France, China, India and Pakistan. Israel is also believed to have nuclear weapons, but it is not clear whether it has tested them.
The established nuclear powers - with half an eye on Iran - were quick to condemn the North Korean action. The White House labelled it a "provocative act" and called for immediate action from the UN Security Council. Tony Blair called it "completely irresponsible".
The two Koreas, which fought a 1950-53 war that ended in a ceasefire but no peace treaty, are divided by the world’s most heavily armed border. But they have made strides toward reconciliation since their leaders met at their first-and-only summit in 2000, since when Seoul has sent regular aid shipments.
North Korea has relied on foreign aid to feed its 23 million people since its state-run farming system collapsed in the 1990s following decades of mismanagement and the loss of Soviet subsidies.
The South Korean Defence Ministry said that the alert level of the military had been raised in response to the claimed nuclear test, but that it noticed no unusual activity among North Korea’s troops.
The repercussions of North Korea’s announcement also were felt in financial markets, sparking plunges in South Korea’s stocks and its currency, the won.
North Korea pulled out of the Nuclear Non-Proliferation Treaty in 2003 after US officials accused it of running a secret nuclear programme that violated an earlier bilateral agreement. For the past year it has boycotted six-nation talks, hosted by Beijing, designed to bring it back into the fold.
In Pyongyang, North Koreans went about their lives as usual today with no signs of heightened alert by security forces. Red flags of the North’s Korean Workers’ Party draped buildings and lampposts to mark Tuesday’s 61st anniversary of the party’s founding.
The country’s state television read the official report about the test during a regular newscast, although the item was not the top story and there were no images shown of the test.
