North Korea presents one of the most dangerous security threats in the world today. This has long been recognised and it did not require another nuclear detonation by the regime of Kim Jong Un to prove the point. It remains unclear whether this week’s explosion involved a hydrogen bomb, as Pyongyang boasts, a move that would represent an alarming advance in its weapons capability. Even so, its decision to conduct the fourth underground test in nearly a decade shows how serious, and yet intractable, the North Korean dilemma has become.

For more than two decades, the US and the international community have used carrots and sticks to try to persuade Pyongyang to curb its nuclear ambitions. In 1994, President Bill Clinton’s administration signed a deal with the North Koreans under which they agreed to freeze plutonium production in exchange for economic co-operation. That deal fell apart in the early years of his successor George W Bush, partly because of American claims that North Korea had reneged on the bargain.

In recent years, the US and other powers have shifted to a tougher approach, punishing the regime with sanctions each time it defies international norms on nuclear non-proliferation. The UN Security Council may continue with this line, imposing new penalties after North Korea’s latest provocation. Far from deterring the rogue regime, such punishment has compounded both its feeling of isolation and sense of resolve. This makes it even harder to come up with an effective reply to its action this week.