UNITED NATIONS (Reuters) - The U.N. Security Council voted unanimously on Saturday to impose financial and weapons sanctions on North Korea for its claimed nuclear test in a resolution that Pyongyang's envoy swiftly rejected as "gangster-like”.

The U.S.-drafted resolution, which said the Communist state's action was a "clear threat to international peace and security," allows nations to stop cargo going to and from North Korea to check for weapons of mass destruction or related supplies.

In a concession to China, the resolution specifically excludes the use of force, but allows economic sanctions and restrictions on naval and air transport. U.S. President George W. Bush told reporters that the resolution showed "the world is united in our opposition to its nuclear weapons plans."

North Korea's U.N. ambassador Pak Gil Yon walked out of the council after he spoke. He accused members of "gangster-like" action for adopting the resolution and ignoring the threat from the United States against his country.

Pak said Pyongyang considered any further U.S. pressure a "declaration of war." North Korea has issued similar statements before, but this time it was before the Security Council.

In Washington, a preliminary U.S. intelligence analysis showed radioactivity in air samples collected near the suspected nuclear test site, a U.S. official said on Friday, five days after Pyongyang announced it conducted the test.

The resolution was adopted after the United States, Britain and France made some modifications after last-minute objections from Russia and China, but in general the original U.S.-proposed sanctions remained intact.

The resolution requires all countries to prevent the sale or transfer of materials related to Pyongyang's unconventional weapons programs. And it demands nations freeze funds overseas of people or businesses connected with North Korea's nuclear and ballistic missile programs.

It drops a ban on all arms going to North Korea, but puts an embargo on all large-sized conventional arms.

"China strongly urges the countries concerned to adopt a prudent and responsible attitude in this regard and refrain from taking any provocative steps that may intensify the tensions," Beijing's U.N. ambassador, Wang Guangya, said.

With China fearing a flood of refugees from a collapse of North Korea -- which was sorely tested yet survived the demise of the Soviet Union, the death of its founder and a famine that may have killed 10 percent of its people in the 1990s -- some questioned what impact any sanctions would have. "North Korea is already very familiar with poverty," former South Korean President Kim Dae-jung told Reuters in an email interview. "The country can also get support, at least in order to survive, from countries such as China."

Kim, the architect of South Korea's engagement policy with the North, blamed U.S. policy in part for the nuclear crisis, which he said could only end if Washington held direct talks with Pyongyang, which the Bush administration rejects. "The United States must talk to North Korea," Kim said. "We have to talk not only with friends but also with enemies, if necessary."

U.S. Secretary of State Condoleezza Rice will visit China, Japan and South Korea from Oct. 17 to 22. A U.S. official said Rice would also likely travel to Russia during the trip.

Japanese Prime Minister Shinzo Abe immediately said Tokyo would consider further punitive steps against North Korea.

In Tokyo, Shoichi Nakagawa, chairman of the ruling Liberal Democratic Party (LDP)'s Policy Research Council, said Japan will adhere to its policy of not arming itself with nuclear weapons in response, but added that a debate on the issue was necessary.

In Seoul, the South Korean Foreign Ministry said on Sunday that it would "faithfully implement" the resolution. But South Korea has said it would not pull the plug on its two main projects in the North -- an industrial park and a mountain resort -- that supply a steady stream of cash to Pyongayng's leaders.