North Korea's latest move has stoked anger south of the border
By John Sudworth
BBC News, Seoul
North Korea has, with typical aplomb, delivered the world another challenge regarding its nuclear weapons programme.
The past 12 months have had challenges enough.
First came the announcement that North Korea planned to restart reprocessing spent fuel rods from its nuclear reactor - the only method which it has admitted to using to build its atomic stockpile so far.
Then came its decision to walk away, for good it said, from the long-running nuclear disarmament talks, as well as the kicking-out of the United Nations nuclear inspectors.
And finally, its underground nuclear detonation, an act that sent shockwaves, quite literally, beyond North Korea's borders.
But now comes the news that it may be on the brink of building itself a new path to the nuclear bomb - uranium enrichment.
Pyongyang's claim that its scientists have successfully carried out the process has been met with alarm in South Korea.
Uranium enrichment is much easier to conceal than plutonium reprocessing.
You don't need a large nuclear reactor, just a laboratory, so it can be done away from the prying eyes of spy satellites.
And, adding further concern, North Korea has ample natural reserves of the raw material.
In fact, the process would offer Pyongyang such a convenient method of building a bomb, that you might wonder why it has not been tried already.
Well, some have been wondering exactly that, for quite a long time.
N Korea's Yongbyon plant is thought to be the heart of its nuclear operations
The allegation that North Korea was already enriching uranium first surfaced in 2002.
The country's foreign minister is reported to have acknowledged the existence of the programme to visiting US officials.
But it has consistently denied such claims ever since, at least until June of this year.
Within hours of the imposition of new UN sanctions - punishment for its underground nuclear test - North Korea said it would begin trying to enrich uranium.
It should take several years to develop a full-scale programme, so is North Korea's trumpeting of its scientists' newly-acquired know-how, perhaps an admission that it has been working on it all along?
Or is it a bluff?
The claim is, of course, almost impossible to verify, but there is one consideration that should allay at least some of the fears about North Korea's nuclear ambitions.
It is not yet thought to have developed the technology necessary to mount a nuclear weapon on a war-head, much less a reliable long-range rocket system with which to deliver it.
And a uranium-based weapon is even harder to miniaturise than a plutonium-based one.
Whatever the truth of North Korea's claim to be entering the "completion phase" of its experiments with uranium enrichment, the statement does seem to be at odds with its recent behaviour.
During the past few weeks it has been making gestures that many observers see as an attempt to lower tensions.
North and South Korea have relaxed border controls with each other
It has sent a high level delegation to meet the South Korean President in Seoul and it has relaxed some of the restrictions on border traffic crossing from the South, to visit a joint industrial zone.
But there have been warnings of caution, not least from the South Korean government itself, not to read too much into the warmer words and firmer hand-shakes.
The mood music may have changed a little, the argument goes, but North Korea has given no indication that it is ready to return to the disarmament talks, much less give up the pursuit of nuclear weapons.
Pessimists doubt whether this has ever been Pyongyang's intention, and its claim that its scientists are now deftly spinning uranium enrichment centrifuges around in apparent glee, will confirm them in their view.
Sanctions and talks?
North Korea's statement though, says it is ready for both sanctions and dialogue.
It has long argued that it needs its nuclear weapons programme as a security guarantee against a threat from the US, which it says has been all too ready to practice regime change elsewhere in the world.
And it argues that it has been unfairly treated, being pushed and punished over its nuclear weapons programme, while south of the border, 28,000 US troops are stationed, backed by the military might of a nuclear armed superpower.
Those who are more optimistic about the prospects for getting Pyongyang to give up on the bomb say that any opportunity for dialogue should be seized.
Despite ongoing tensions, dialogue remains open between north and south
Shortly before he died last month, I recorded the last broadcast interview with the former South Korean President, Kim Dae-jung.
He was a man whose time in office was defined by his attempts to reach out to the North.
He told me that he believed it was folly to back North Korea into a corner.
And he said that in his view, there had never been a case in history where communism had been defeated by either force or sanctions.