WASHINGTON North Korea's effort to enrich uranium is typical of its defiance of the United Nations, and major powers including China must put pressure on Pyongyang to abandon its nuclear ambitions, senior U.S. officials said on Sunday.
North Korean officials took a U.S. nuclear scientist, Siegfried Hecker of Stanford University, to a plant at its Yongbyon nuclear complex where he saw hundreds of centrifuges that Pyongyang said were installed and operational.
Washington has believed since 2002 that Pyongyang had such an enrichment program, but the apparent sophistication of its effort could ignite fresh debate over how to deal with North Korea's unpredictable leadership and whether to resume talks aimed at ending its nuclear ambitions.
"The notion that they could develop this is obviously a concern, but I would say fairly consistent with their longstanding willingness to ignore the U.N.," Defense Secretary Robert Gates said.
"North Korea has ignored a number of Security Council resolutions and sanctions. They continually try to export weapons in violation of those resolutions," Gates told reporters in Santa Cruz, Bolivia, where he was attending a conference of American defense ministers.
Admiral Mike Mullen, chairman of the military's Joint Chiefs of Staff, said the disclosure showed that North Korea was a "dangerous country" intent on making nuclear weapons and major powers must work together to put pressure on North Korean leader Kim Jong-il.
"We have to continue to bring pressure on him specifically. Those in the region -- in particular the six-party talk countries, Russia, China, the United States, Japan, and South Korea -- we all have to continue to do that," Mullen told ABC television's "This Week with Christiane Amanpour" talk show.
Asked whether this new facility raised concerns the North was making more nuclear weapons "right now," Mullen told ABC: "This certainly gives that potential real life."
The North Koreans told Hecker they had 2,000 centrifuges in operation, but the U.S. team that visited the country was unable to verify that they were working. Hecker said North Korea claimed the program was aimed at generating electricity.
Gates dismissed the notion the enrichment program might be for energy production, saying North Korea had an ongoing nuclear arms program for some time and probably had a number of nuclear devices.
"I believe they have nuclear weapons, they're clearly developing longer-range missiles, including potentially a mobile ICBM (intercontinental ballistic missile), so all of these programs are of great concern to every nation," he said.
Gates said he had "no idea" what motivated North Korea to reveal the plant at this time, and he declined to discuss U.S. options going forward, saying the incident occurred while he was out of the country and he needed to consult first with other U.S. security and diplomatic officials.
By showing off its nuclear hand, analysts say North Korea is seeking to gain leverage in any aid-for-disarmament negotiations in stalled six-way talks with regional powers China, Japan, South Korea, Russia and the United States.
Its nuclear program is seen as a threat to U.S. allies Japan and South Korea, and a proliferation risk given North Korea's long history of selling missile technology abroad.
The top U.S. envoy on North Korea arrived in Seoul late on Sunday to discuss with key Asian nations ways to thwart Pyongyang's nuclear ambitions.
Mullen singled out China -- North Korea's closest ally -- saying Beijing would necessarily have "an awful lot to do with" future attempts to sway Pyongyang.
"We've been engaged with China for an extended period of time with respect to North Korea ... a great part of this, I think, will have to be done through Beijing," he told ABC.
Mullen put the nuclear disclosure in context by pointing to the March sinking of a South Korean warship, which Washington and Seoul blame on Pyongyang. The suspected torpedo attack killed 46 South Korean sailors and stoked tensions on the peninsula.
"All of this is consistent with belligerent behavior -- the kind of instability creation in a part of the world that is very dangerous," Mullen said.
The North's reported nuclear advances come nearly two months after Kim Jong-il started the transition of power to his youngest son, Kim Jong-un. Analysts say he wants to use nuclear muscle to boost his son's credentials with the military.
"And, in fact, I also believe that this has to do with a succession plan for his son," Mullen said.
(Additional reporting by Arshad Mohammed in Washington, David Alexander in Santa Cruz, and Jeremy Laurence in Seoul; Editing by Stacey Joyce)