U.S. Calls North Korea's Nuclear Revelation a 'Publicity Stunt'

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The United States today called North Korea's decision to unveil a new uranium enrichment program to a group of visiting American scientists a "publicity stunt" and said it will take some time to consult with allies about how to proceed.

"The fact that North Korea invited these scientists to come to Pyongyang and did a show-and-tell, that by itself is valuable information. We'll compare that with other things that we know, and we'll make a formal assessment as to what we think, you know, this capability represents and what the implications are," State Department spokesman P.J. Crowley told reporters.

Questions remain, however, about how the capability and intentions of North Korea's uranium program, as well as its origins. On Sunday, Defense Secretary Robert Gates suggested the facility had been unknown to the United States.

"I hadn't known about this specific facility before, but the fact that they were going -- that they wanted their own enrichment capability is not a surprise," Gates said.

Hours before the news broke Saturday the Obama administration scrambled its top North Korea negotiator, Ambassador Stephen Bosworth, to consult with allies in Asia as it tries to chart a response.

Today the State Department spokesman suggested it would not provide further incentives for North Korea to return to the negotiating table.

"We will not be drawn into rewarding North Korea for bad behavior," Crowley said. "They frequently anticipate doing something outrageous or provocative, and forcing us to jump through hoops as a result. We're not going to buy into this cycle."

Last week a team of American scientists, led by Siegfried Hecker of Stanford University, returned from a trip to North Korea during which they were invited to visit a previously undisclosed nuclear facility that North Korea says is capable of enriching uranium.

The North Koreans claim the facility is meant to produce fuel for an electric power plant, but the United States fears it could be used to further Pyongyang's nuclear weapons ambitions.

Gates yesterday expressed doubts about North Korea's intentions.

Scientist 'Stunned' by Facility's Sophistication

"I don't credit that at all," he told reporters traveling with him in Bolivia.

In an interview with the New York Times, which first reported the scientists' findings on Saturday, Hecker said he was "stunned" by the sophistication of the facility.

Hecker said he was shown a room full of "hundreds and hundreds" of recently installed centrifuges and manned by "an ultra-modern control room." The North Koreans claimed 2,000 centrifuges were already operating at the facility, he said.

Robert Carlin, another Stanford university expert who was on the trip to North Korea, told ABC News Sundday that the facility they were shown was well beyond the capacity they had believed the North Koreans possessed.

"Everyone thought they were still at a very early stage, maybe past experimental but just beginning to move into a more serious production," he said.

According to a full version of Hecker's report, which was shared Monday with ABC News, "the uranium enrichment facility was ultra-modern and clean."

Though enriching uranium to weapons-grade is technically challenging, "the uranium enrichment facilities could be readily converted to produce highly-enriched uranium (HEU) bomb fuel," the report said.

According to the report, North Korea almost certainly received outside help in producing the facility, likely from Pakistan and perhaps also from Iran, which has been pursuing its own uranium enrichment program.

The Obama administration today called on North Korea to halt its nuclear program and return to negotiations, but declined to say if it would pursue another round of sanctions in the United Nations Security Council.

"We do not at all rule out the possibility of further engagement with North Korea, but we want that to take place under a proper set of conditions and in close coordination with our partners," Bosworth said after meetings in South Korea today.

"I do not believe in engagement just for the sake of engagement or talking just for the sake of talking. We have to begin to make progress," he said. "And it is fundamental that the North Koreans demonstrate that they approach the dialogue and the discussions and the negotiations with that same measure of seriousness and willingness to actually take hard decisions."

North Korea Nuclear Plant Part of Ongoing Argument

North Korea has already been slapped with U.N. sanctions, most recently after its nuclear weapons tests in 2006 and 2009. It is believed that North Korea has produced enough material from its plutonium program for roughly eight to 10 nuclear weapons.

North Korea has only acknowledged a plutonium nuclear program, which reprocesses spent fuel from a nuclear reactor. The facility unveiled last week is potentially another path to a nuclear bomb, in which uranium is enriched in complex spinning centrifuges, similar to the program Iran has been pursuing.

The United States says that in 2002 North Korea confessed to, and then denied, having a uranium enrichment program. The top American military official said Sunday that the revelation justifies America's concerns that program endured.

"This validates a long-standing concern that we've had with respect to North Korea and -- and its enrichment of uranium," Admiral Mike Mullen, the chairman of the Joint Chiefs of Staff, told ABC News' Christiane Amanpour on 'This Week.'"

Republicans, who will take control of the House of Representatives when the new Congress begins next year, were quick to pounce on the news as a failure of the Obama administration's engagement policy with North Korea.

"The administration's policy of outreach to the North Korean regime has clearly failed. It is time to get tough if North Korea is to be prevented from continuing to expand its nuclear weapons capability," Rep Ileana Ros-Lehtinen, the incoming chair of the House Foreign Affairs Committee, said in a statement.

Last December, the Obama administration sent Bosworth to Pyongyang to meet with the North Koreans. Bosworth carried with him a letter from President Obama to North Korean leader Kim Jong Il.

The so-called Six Party Talks, consisting of the United States, China, Russia, Japan, South Korea, and North Korea, have been stalled since the end of the Bush administration, after North Korea reneged on verbal promises to take steps to disable its nuclear program.

Those promises had led to North Korea being removed from the State Sponsor of Terrorism list in October 2008.

Rep. Ros-Lehtinen: 'Time to Correct this Mistake'

"Pyongyang's removal from the list two years ago as a reward for cosmetic actions on one component of its nuclear activities was a grave error. It is time to correct this mistake," Ros-Lehtinen said.

ABC News' Jim Sciutto contributed to this story.