"There's no doubt we have been flexible in looking for alternatives," Bolton told reporters after meeting Chinese vice foreign ministers to discuss North Korea's standoff with Washington over Pyongyang's nuclear ambitions.

"But ultimately if the Security Council is to remain a venue where these kinds of issues can be addressed, not being able to address the North Korean issue would be a grave impairment of the Council...," he said.

It "would mean that it was not only incapable of addressing North Korea but may well be impaired from addressing other proliferation issues or other threats to international peace and security as well."

The US undersecretary of state for arms control and international security warned that countries that opposed taking up the issue in the Council "face the marginalization of the Security Council on this critical issue".

"So those who say that the Security Council is not the appropriate place to go have to take into account the impact of their statement and the long-term significance and potential role of the council in a variety of disputes," he told a news briefing.

Bolton urged the five permanent members of the Council -- which besides the United States are China, Russia, Britain and France -- to consider addressing the North Korean issue in the Council.

China and Russia have opposed using the UN body as a means to resolve the nine-month standoff, as it could lead to sanctions. Pyongyang has warned it would consider sanctions a declaration of war.

When asked whether it would support any UN Security Council action on North Korea, China has said it did not support any actions that would complicate the North Korean standoff.

Bolton said he discussed with Chinese leaders Monday the possibility of using the Security Council as a means to deal with the crisis, but did not reveal whether he detected any changes in Beijing's attitude.

Bolton added that Washington had been flexible and open to exploring other ways of resolving the crisis over Pyongyang's nuclear ambitions, and proceeding in the Security Council was only one of the options Washington was considering.

He said another option was denying North Korea the hard currency earnings it used to fund its nuclear weapons program.

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