US and Asian officials with access to the latest intelligence on North Korea say strong evidence has emerged in recent weeks that the country has built a second, secret plant for producing weapons-grade plutonium, complicating both the diplomatic strategy for ending the program and the military options if that diplomacy fails.
The discovery of the new evidence, which one senior Bush administration official cautioned was "very worrisome, but still not conclusive," came just as North Korea declared to the US 12 days ago that it had completed reprocessing 8,000 spent nuclear fuel rods, enough to make a half dozen or so nuclear weapons.
US officials have said they cannot verify that claim, though they confirm that sensors set up on North Korea's borders have begun to detect elevated levels of krypton 85, a gas emitted as spent fuel is converted into plutonium.
What concerns American, South Korean and Japanese analysts, however, is not simply the presence of the hard-to-detect gas but its source. While US satellites have been focused for years on North Korea's main nuclear plant, at Yongbyon, the computer analyses that track the gases as they are blown across the Korean Peninsula appeared to rule out the Yongbyon reprocessing plant as their origin. Instead, the analysis strongly suggests that the gas originated from a second, secret plant, perhaps buried in the mountains.
US officials have long suspected that North Korea would try to build a second plant to protect itself against a pre-emptive strike by the US. The US even demanded an inspection of one underground site five years ago, only to find it empty, but this is the first time evidence has emerged that a second plant may be in operation.
"This takes a very hard problem and makes it infinitely more complicated," said one Asian official who has been briefed on the US intelligence. "How can you verify that they have stopped a program like this if you don't know where everything is?"
Indeed, there may now be at least two hidden facilities with the capacity to produce material for nuclear weapons. In October, confronted with US evidence, North Korean officials admitted that they had clandestinely built a plant intended to produce uranium, another fuel for a bomb. (It is the same approach former Iraqi president Saddam Hussein tried in the early 1990s, and that Iran is pursuing today.) US officials say they have never found that plant, though they believe it is still a few years away from full-scale production.
If it turns out that the current evidence is being properly interpreted, and a second plutonium plant also exists, President George W. Bush may not even have the option that then president Bill Clinton briefly considered in 1994: using a military strike or sabotage to prevent North Korea from producing significant amounts of weapons-grade material. Still, Bush has vowed that he "will not tolerate" a nuclear North Korea.
US intelligence officials say they are wary about making any final judgments about the new evidence. They are keenly aware that CIA assessments of Iraq's nuclear program have touched off a national debate over whether intelligence was exaggerated, and have made all the agency's findings suspect.
That issue has also put the White House at odds with CIA Director George Tenet, who knows that the White House is going to extraordinary lengths to avoid calling the nuclear confrontation with North Korea a crisis. So far, White House officials have been told only informally of the new evidence and have not been fully briefed about its potential implications, administration officials say.