North Korea has threatened to carry out a second nuclear test unless the United National Security Council apologises for criticism of its rocket launch earlier this month.

The threat raises the stakes in Pyongyang’s strategy of brinkmanship with the international community, coming days after the isolated Stalinist state announced that it had restarted extracting plutonium from spent fuel rods at its nuclear plant.

North Korea’s Foreign Ministry said that the country would be compelled to take additional "self-defensive measures" unless the Security Council apologised immediately. “The measures will include nuclear tests and test-firings of intercontinental ballistic missiles," it said.

Such an escalation of tension in the region will infuriate China, the North’s only real international friend. Beijing could scarcely conceal its rage when Pyongyang unexpectedly carried out a nuclear test in 2006. It was also clearly frustrated when Pyongyang carried out the rocket launch on April 5 that other governments described as a disguised long-range missile test.

North Korea seems determined either to develop an atomic arsenal or push the US into direct talks while giving it a stronger hand in any dialogue – or perhaps both.

The Security Council imposed sanctions on North Korea after the launch of a ballistic missile in July 2006 and a nuclear test a few months later. After this month's rocket launch, it called for the sanctions to be tightened. The impoverished North has lashed out at the measures, saying that it would boycott six-country disarmament talks and bolster its nuclear deterrent.

Zhang Liangui, an expert on the North at the Central Party School in Beijing, said: “The fundamental fact is that North Korea is set on becoming a nuclear power and, to accomplish that, more tests are needed. One nuclear test isn't enough. There'll be more nuclear tests and more missile tests."

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