What Does North Korea Want?

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But there was another explanation for the announcement: Pyongyang needed to change the subject. Two weeks ago, the White House secretly dispatched two National Security Council (NSC) aides to Tokyo, Beijing and Seoul armed with evidence that North Korea may have supplied a uranium compound to Libya for its weapons labs. The gaseous compound, known as uranium hexafluoride (UF6), is a precursor to bomb-grade uranium, something bombmakers feed into centrifuges to harvest the highly fissionable isotope uranium-235 (U-235) that is at the heart of an atom bomb. Though UF6 is hard to make, it's possible to track: forensic tests focus on trace isotopes, such as U-234, whose prevalence differs from country to country and even from mine to mine. After the U.S. gained access to Tripoli's bombmaking labs a year ago, it ran tests on the UF6 it found there. U.S. officials would not connect all the dots, but one told TIME the fuel from Libya bore "a very clear signature" that pointed to North Korea.

The new U.S. evidence was rushed to officials in Beijing, who have tolerated Pyongyang's denials that it has a UF6 processing facility. The U.S. intelligence made that view seem dangerously naive. If North Korea was producing enough UF6 to export to Libya, it surely had enough for its weapons labs at home. There is some evidence that North Korea sold its UF6 not directly to Libya but via the black-market bazaar of Pakistani scientist A.Q. Khan. That means that North Korea may not have known where its UF6 was going when it sold it, says Gordon Flake, a North Korea analyst at the Mansfield Center for Pacific Affairs. The new UF6 evidence was apparently strong enough to help the two NSC aides, Michael Green and William Tobey, win an audience with Chinese President Hu Jintao two weeks ago. U.S. officials would not detail Hu's reaction to the briefing, but one told TIME, "It made an impression."

But that hasn't led to much clarity about what to do. Two questions occupy the Bush team's sometimes highly divided proliferation squads: Just what is the nature of Pyongyang's arsenal? And what, if anything, can be done about it? The type and number of weapons Kim has remain unknown. Most analysts think the count is fewer than a dozen. Size actually matters more than quantity: the smaller the warhead, the easier it is to mount it in an airplane or atop a missile. Several of Pyongyang's medium-range systems, if operational, could reach Japan; one long-range weapon could theoretically reach Alaska.