International authorities have for years used export and trade sanctions to keep North Korea from building a nuclear weapon; just today, Chinese officials posted 236 pages of materials barred from export to the North. But such methods might be pointless: Pyongyang appears capable of making important centrifuge parts on its own turf, US experts say—a capability it's had since 2009 at the latest. "If they're not importing these goods in the first place, then we can't catch them in the act," a nuclear proliferation expert tells the AP.
"We won't necessarily see anything more than what the North Koreans want us to see," he adds. In an upcoming report, researchers cite several pieces of "strong and clear" evidence for their theory. For one thing, in the early 2000s, Pyongyang was importing quantities of centrifuge parts; that seems to have stopped. State media photos show centrifuge-building equipment, while media and scientific reports and propaganda suggest progress. (Read more North Korea stories.)