"I think it would be fair to say that if, at some point, North Korea continues to stonewall, then I think the Security Council is the next logical step," said US under secretary of state for arms control and international security 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, speaking to reporters after addressing an American Enterprise Institute forum, 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.

Bolton's remarks Tuesday came a day after a North Korean minister claimed that Pyongyang had turned plutonium from 8,000 spent nuclear fuel rods into weapons to serve as a deterrent against a possible nuclear strike by the United States.

"We have already declared that we have reprocessed 8,000 wasted fuel rods and weaponized them," North Korean Vice Foreign Minister Choe Su-Hon told journalists in New York.

Choe's remarks were unprecedentedly explicit. Pyongyang has previously used vague terms such as "nuclear deterrent" to refer to its capability.

Reacting to the remarks, US State Department spokesman Richard Boucher said North Korea should stop boasting and return to the negotiating table.

"We've seen a whole series of claims from the North Koreans about "watch out, we're doing this; watch out we're doing that," Boucher said.

"That doesn't alter the fundamental situation," he said, adding that North Korea had "violated its commitments, continued to violate its commitments, is bragging about violating its commitments and its promises."

He said Pyongyang had also alienated its neighbors in northeast Asia.

The United States, Boucher said, had been "very clear and very consistent" over the nuclear issue and had wanted North Korea to return to the six-party talks so that a way could be found to resolve the crisis.

The United States had proposed an aid-for-disarmament plan for North Korea at the previous round of talks but Pyongyang had rejected it, saying Washington was not sincere.

Bolton said the United States expected "a serious answer" from North Korea on the plan.

He said that "obviously" the fourth round would not take place this month.

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