Leading article: North Korea returns to its game of nuclear blackmail

So closed is Pyongyang that it is impossible to say with any certainty what North Korea's bellicose gestures towards the outside world indicate about the internal politics of the regime. Yesterday's underground nuclear test has been interpreted by some as evidence of a power struggle sparked by Kim Jong-il's recent stroke. Another theory is that the regime conducted the test to cover up the embarrassment of its failed long-range missile launch last month.

Either explanation could be true; or both could be wide of the mark. The unfortunate reality is that there exists no North Korean "Kremlinology" with which to analyse power shifts in the upper echelons of the regime. Interpretations of North Korean politics are based to a large extent on educated guesswork. However, what we do know is that whenever North Korea is in danger of slipping off the international agenda, Pyongyang tends to pull a stunt like this to reclaim the world's attention. In the absence of any other evidence to the contrary, we have to assume that North Korea is playing its traditional game of nuclear blackmail.

The question is: how should the region and the wider world respond to such provocation? Global leaders were, once again, united in condemnation of the North's behaviour yesterday. Barack Obama warned that Pyongyang "will not find international acceptance unless it abandons its pursuit of weapons of mass destruction". These sentiments were echoed in Russia, China and across Europe. And an emergency meeting of the United Nations Security Council censured Pyongyang.

But the truth is that the international community's options are limited when it comes to dealing with North Korea. The application of military force carries too many risks. The North Korean regime is dysfunctional but, with its million-strong army, it still has the capacity to inflict horrific damage on any invading force. Moreover, the South Korean capital, Seoul, lies well within missile range of the North's artillery. A repeat of the 1950-53 war could trigger the very nuclear catastrophe the West seeks to prevent.

As for sanctions, they have been shown to be ineffective. The Bush administration tried squeezing Pyongyang in this way in the former president's first term, only for Pyongyang's first successful nuclear test back in 2006 to force Washington back to the negotiating table.

And, of course, the drawbacks of diplomatic engagement have been plain for all to see too. The world has been promising Pyongyang aid in return for disarmament for more than a decade, yet still it finds itself menaced by this throwback Stalinist regime. And, ominously, there are even signs that China is losing influence over its former Communist ally.

Yet the world has no other viable option but to keep plugging away with the policy of engagement though the Beijing-hosted six-party framework. Of all the approaches available, this is the one that came closest to delivering success when Pyongyang agreed to close its nuclear reactor two years ago. Engagement also offers the most effective means, in the immediate term, of containing the North Korean nuclear threat.

In the longer-term, we must hope that this vicious regime collapses under the weight of its own incompetence and that those nations which have offered the hand of friendship to the people of the North will be able to engineer a peaceful re-unification of the Korean peninsula.