Instead, experts say, it has produced enough plutonium from its fuel rods for possibly up to a dozen nuclear weapons over its 20-year history.

North Korea announced over the weekend that the reactor and other facilities at Yongbyon had been shut down, as part of a six-nation nuclear disarmament deal agreed in February.

The reactor, 96km north of Pyongyang, has a capacity of 5MW and began operating in 1987. Two larger reactors at the same site are not yet thought to be operational, though there is a functioning plutonium reprocessing plant several storeys high.

The five-megawatt reactor is too small to make much difference to the nation's acute power shortage and a US Congressional Research Service (CRS) report in January said it reportedly had no power lines attached to it.

Nevertheless, the North demanded steep compensation for lost energy when it shut down Yongbyon under a 1994 'Agreed Framework' deal with the United States.

An international consortium started work on two proliferation-resistant light water reactors and the US provided an interim 500,000 tonnes a year of heavy fuel oil.

The deal collapsed in 2002, when Washington accused the North of running a covert highly enriched uranium programme, and fuel shipments were suspended.

North Korea denied the charge but restarted Yongbyon after an eight-year shutdown, expelled United Nations atomic inspectors and announced it was leaving the nuclear Non-Proliferation Treaty.

When the reactor is operational, the CRS report said, it can produce about 6kg of plutonium annually, enough for one small bomb.

The latest shutdown, if confirmed, stops the North from producing more plutonium for its stockpile - estimated by the US-based Institute for Science and International Security at 46kg to 64kg.

Some 28kg to 50kg of this is estimated to have been separated, enough for about five to 12 nuclear weapons, the institute said in February.

AGENCE FRANCE-PRESSE