WASHINGTON -- It's official: North Korea tested a nuclear weapon last week, albeit a small one.

"Analysis of air samples collected on October 11, 2006, detected radioactive debris which confirms that North Korea conducted an underground nuclear explosion in the vicinity of P'unggye on October 9, 2006," said a statement from National Intelligence Director John Negroponte's office posted Monday on its Web site.

Negroponte's office also confirmed that the size of the explosion was less than 1 kiloton, a comparatively small nuclear explosion. Each kiloton is equal to the force produced by 1,000 tons of TNT.

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The statement comes at a diplomatically sensitive time. Secretary of State Condoleezza Rice prepares to visit the region as news reports indicated that Chinese customs inspectors had begun inspecting cargo trucks bound for North Korea in the border city of Dandong.

Japan and Australia, meanwhile, announced Monday that they might take measures beyond the new U.N. sanctions.

A U.S.-sponsored resolution at the United Nations passed Saturday demands North Korea eliminate nuclear weapons but rules out military action against the country, as the Russians and Chinese demanded.

After the resolution passed, North Korea's U.N. ambassador accused council members of a "gangster-like" action that neglects the nuclear threat posed by the United States.

Meanwhile, a leading Senate Republican urged direct talks with North Korea, as the reclusive nation has sought. "We do need to engage the North Koreans" because the U.N. resolution is weak and limited, said Sen. Chuck Hagel of Nebraska, the second-ranking Republican on the Senate Foreign Relations Committee.

But Rice brushed aside such calls, reaffirming the U.S. commitment to six-nation disarmament talks, which have stalled.