"I think it would be fair to say that if, at some point, North Korea continue to stonewall, then I think the Security Council is the next logical step," said US under secretary of state for non-proliferation matters John Bolton.

North Korea was referred to the Security Council early last year after it withdrew from the Non-Proliferation Treaty and expelled International Atomic Energy Agency (IAEA) inspectors following Washington's charge that it was involved in nuclear weapons activities.

The council made no decision on the issue.

Later, the United States, the two Koreas, Russia, China and Japan decided to hold six-party talks in Beijing to end the crisis.

Three rounds of talks have been held so far, but North Korea has refused to attend the fourth, scheduled for this month, blaming both US "hostile" policy and secret nuclear experiments in South Korea.

Some reports said Pyongyang wanted to wait for the outcome of the US presidential elections on November 2.

Bolton said "at some point you have to ask the question, if the North Koreans are not willing to engage seriously, what the future of the talks is."

The standoff over North Korea's nuclear ambitions flared in October 2002 when Washington accused Pyongyang of operating a nuclear weapons program based on enriched uranium in violation of a 1994 agreement.

Pyongyang has denied running the uranium-based program but has restarted its plutonium program.

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