Citing unnamed officials familiar with intelligence reports, the newspaper said the Central Intelligence Agency had informed US allies in Asia that American satellites had identified an advanced testing site in an area called Youngdoktong.

At the site, equipment has been set up to test conventional explosives that, when detonated, could compress a plutonium core and set off a compact nuclear explosion, the report said.

Some intelligence officials say they believe that the existence of the testing range is evidence that North Korea intends to manufacture much more sophisticated weapons than previously believed, The Times pointed out.

The new testing capability does not mean North Korea can actually build a small weapon, but it suggests that the North Koreans are moving to combine their two most advanced weapons projects: nuclear technology and missile technology, the report said.

The new intelligence reports suggest that they could develop such a weapon in less than a year, but some officials warn that that assessment represents what one called "a best guess rather than a solid estimate," The Times reported.

According to officials who have been briefed on the American reports, conventional explosions simulating a nuclear detonation have been set off at the testing site, which is near North Korea's main nuclear complex, the paper said.

North Korea has never tested a nuclear weapon, though the CIA believes it has manufactured one or two crude devices.

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