SEOUL, Oct 18 (Reuters) North Korea could push the stakes in its nuclear crisis even higher by unloading spent fuel rods from its sole operating atomic reactor and increasing its stockpile of weapons-grade plutonium, experts said.

North Korea has said the UN sanctions imposed after its test of a nuclear device last week were tantamount to a declaration of war.

One way to show its defiance, short of another test, may be to shut down the reactor to extract more fissile material.

''It'll be a way to show the North is committed to building nuclear weapons,'' Baek Seung-joo, head of North Korean military studies at the South's Korea Institute for Defence Analyses said.

North Korea's nuclear programme is centred in Yongbyon, about 100 km (60 miles) north of Pyongyang, where it has the nuclear reactor and a plant to reprocess plutonium from spent fuel.

The New York Times this week quoted US intelligence officials as saying North Korea's October 9 nuclear blast was caused by plutonium harvested from the Yongbyon reactor.

North Korea said in May 2005 it temporarily shut down Yongbyon to extract fuel rods, which proliferation experts said could provide it with enough material for two or three atomic bombs.

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