In its most explicit assertion yet that it had the bomb, the erratic and secretive Marxist regime bizarrely declared that it had "manufactured nukes for self-defence", and now planned to increase this arsenal. Moreover the North was "suspending for an indefinite period" its participation in the six-nation talks with the US, Russia, Japan, South Korea and China.
"We've heard this kind of rhetoric before," said Scott McClellan, the White House spokesman, insisting that the US remained committed to "a peaceful, diplomatic resolution" to the North Korean nuclear dilemma. China too expressed the hope the Pyongyang would return to the bargaining table.
Others speculated that the move was in response to the naming of North Korea by the incoming Secretary of State, Condoleezza Rice, as an "outpost of tyranny" during her Senate confirmation hearings last month.
Almost certainly too, it reflects Pyongyang's irritation with reports here that a White House emissary travelled to Beijing last week to deliver a message from President George Bush to the Chinese government about the North, along with evidence that the regime had supplied nuclear materials to Libya. Most unusually, the official - Michael Green, director for Asia at the National Security Council - was received in person by President Hu Jintao.
Whatever the truth, yesterday's bellicose statement was a blunt reminder that North Korea is by far the most immediate danger to global nuclear stability, and a prime likely culprit in the nuclear proliferation whose prevention is the number one priority of American foreign policy.
Iran is scolded almost daily by the Bush administration for its suspected nuclear arms programme. But most experts reckon it is still two or three years away from acquiring a deliverable nuclear weapon. But North Korea, which was virtually unmentioned by the President in recent months, is quite another matter.
Though it has never tested a weapon (a move widely seen as the logical next step in the country's confrontation with the West), the country may have produced enough plutonium from spent reactor rods to make six or eight nuclear devices. But US intelligence has been unable to establish the truth. As Donald Rumsfeld, the Defence Secretary, admitted yesterday, though the situation was "very worrisome", the US simply did not know for certain whether Pyongyang actually possessed weapons. In fact North Korea has two nuclear weapons programmes. One is based on plutonium extracted from spent fuel rods at its Yongbyon reactor. In 2003, the Natural Resources Defence Council guessed that it had up to 9kg of plutonium, enough for four or five nuclear devices, and that quantity is presumed to have increased since United Nations inspectors were ejected from the country at the end of 2002.
That action followed Pyongyang's stunning admission in October 2002 that in defiance of every previous undertaking, it was pursuing an enriched uranium programme, based on technology obtained from Pakistan, and using North Korea's own substantial deposits of uranium.
During his mission to Beijing, Mr Green is understood to have presented Chinese leaders with evidence that - wittingly or otherwise - Pyongyang supplied Libya with uranium hexafluoride, a chemical that can be processed to yield weapons-grade enriched uranium.
According to officials quoted by The New York Times, the uranium containers had traces of plutonium whose "signature" matches a sample of North Korean plutonium in the possession of the US.
The US strategy, officials here say, is to make sure that China is on "the same side of the issue" as Washington, in the event that negotiations conclusively break down.
That in turn reflects the painful truth that the US has no good options for dealing with the North. Military action of the type taken against Iraq and mooted against Iran would almost certainly trigger an all-out war on the Korean peninsula, American experts say, with potentially a million or more casualties.
Despite international anxiety over the Iranian and North Korean nuclear programmes, and the mounting risk of proliferation, the celebrated "Doomsday Clock" of the Bulletin of the Atomic Scientists remains at seven minutes to midnight, where it has stood since 2002.
"North Korea's announcement today doesn't necessarily change anything, since they're believed to have had weapons for several years," Stephen Schwartz, the Bulletin's director said. "But nuclear dangers are clearly growing."
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