Rupert Cornwell: America is stretched in the war on terror, and its options over Pyongyang are limited

The move had been anticipated - a well-nigh inevitable climax to years of failed diplomacy

It is unrecorded whether the famously early-to-bed US President had to be woken from his sleep when his national security adviser, Stephen Hadley, brought the news at 10pm on Sunday. But the announcement by North Korea that it had just carried out its first nuclear test can surely have come as no surprise for George Bush.

Ever since last Tuesday, when Pyongyang said it planned a test and US satellites detected unusual activity at the suspected site in the north-east of the country, diplomatic speculation had been intense that a test was imminent. But in the longer term too, the move had been anticipated - a well-nigh inevitable climax to years of failed diplomacy between the world's lone superpower and the paranoid, obsessively secretive Communist regime that governs the northern half of the Korean peninsula. In the end, one senior US diplomat said yesterday: "There was just no stopping them."

Ever since Pyongyang in 1993 declared it would leave the Nuclear Non-Proliferation Treaty, the White House has wrestled how to deal with the challenge posed by North Korea, as a nuclear armed state that would threaten not only America's close ally South Korea, where up to 37,000 US troops are based, and whose new weapons would raise the spectre of a wider nuclear arms race in east Asia.

Bill Clinton offered a deal, of two peaceful nuclear power stations and other aid to North Korea in exchange for a freeze, and subsequent abandonment, of Pyongyang's nuclear weapons programme. In 1999 the US went so far as to relax sanctions, and in 2000 Madeleine Albright became the first secretary of state to visit the North. But the agreement fell apart amid mutual accusations of backsliding, and when Mr Bush became President the following year, hard-liners in the new Republican administration resolved on a much tougher line, rejecting all contact with the Communist regime in Pyongyang until it demonstrably scrapped its weapons programme.

Then came 9/11 and Mr Bush's naming of North Korea in his 2002 State of the Union address as a member alongside Iraq and Iran of the "axis of evil".

But in late 2002, with the world's attention fixed on the impending US invasion of Iraq, North Korea staged its own pre-emptive strike, expelling the remaining United Nations inspectors and departing from the NPT, this time for good.

The past three years have seen a variety of initiatives, most notably a framework of six-nation talks that in late 2005 fleetingly seemed to have extracted a promise by the North to give up its quest for nuclear weapons.

However, those hopes faded after barely 24 hours. The six-nation process came to a standstill. A North Korean nuclear test, demonstrating Pyongyang's refusal to capitulate to what it saw as a US-orchestrated campaign to destroy its regime, was the logical outcome.

The basic point of disagreement was ostensibly merely one of timing. The North insisted that the US must sign a non-aggression pact and a comprehensive aid package before it ended its nuclear programme. For Washington, it was exactly the other way around; first the North had to scrap its quest for weapons, and only then would it hold bilateral talks about an economic and security package.

But that stern line masks uncomfortable truths, which Mr Bush tacitly acknowledged in his statement. The President's language was outwardly uncompromising: the North's behaviour had been "provocative" and "unacceptable". Most important, he declared that Washington was still committed to diplomacy. As he had to, because even the mightiest nation on earth, has no good military options.

Like his predecessor Mr Clinton (who came close to ordering strikes on the North's nuclear sites), Mr Bush has concluded, however reluctantly, that there is no good military option - short of an inconceivable nuclear strike to obliterate not just the nuclear programme but North Korea's huge conventional forces as well. Anything less would trigger war on the Korean peninsula, the most heavily armed region on the planet where 1.2 million North Korean troops deployed against a 650,000-strong force from the South.

Despite the 1953 armistice that ended the 1950-1953 Korean War, no peace treaty has been signed. Seoul, the South Korean capital, is within artillery range of the border, and would be effectively impossible to defend in the event of an attack by the North. The US, desperately stretched by the conflicts in Iraq and Afghanistan, but which still has 30,000 troops in the South, would be dragged into a major ground war. But if a military solution is not feasible, the diplomatic route will scarcely be simpler.

Washington is demanding immediate action by the UN. Whether China and Russia, both veto-wielding powers in the Security Council, will agree to meaningful sanctions is doubtful. China, supplier of energy and food to the North, has more leverage than anyone. But if there is one thing Beijing fears more than a nuclear North Korea, it is a failed North Korea.

Somehow Washington must square this circle and dissuade Japan, South Korea and Taiwan from seeking their own nuclear weapons. In the end there may be no alternative to what the Bush administration has said it will never do - negotiate. "It is not appeasement to talk to your enemies," James Baker, secretary of state under the first President Bush, said at the weekend. Mr Baker was referring to Iran and Syria. But his words could apply equally to North Korea.