Testing the Limits

In the late 1990s, U.S. spy satellites probing North Korea picked up evidence of work on a secret underground nuclear test facility. But when U.S. officials were allowed to inspect the site in 1999, they found an empty hole. Now, new images appear to show the North Koreans hard at work on another suspicious tunnel, this time in the northeastern Kilju county. Heavy equipment has been spotted hauling material into the hole, according to a U.S. official briefed on the latest intelligencea possible sign that the North is plugging the shaft to create an underground chamber for an imminent nuclear...