Originally Posted by PC Dave

Colin Powell issued an official statement denying it was a nuke. Some believe that if the administration says something it's by definition a lie; here's another perspective from Strategypage:

KOREA: Mushroom Clouds Over the North

September 12, 2004: The large explosion in North Korea was apparently not nuclear, as this would have registered on seismographs (earthquake detectors) throughout the region. It is common for large conventional explosions to create mushroom shaped clouds. This was the case with the U.S. Air Forces MOAB ten ton bomb. When tested in Florida last year, the explosion produced a prominent mushroom shaped cloud. MOAB's smaller predecessor, the daisy cutter, was used in Kuwait during the 1991 war, also produced a mushroom shaped cloud, and sparked rumors of nuclear weapons use. It is also common for explosions in chemical or ammunition plants, or in weapons storage facilities, to produce explosions that form mushroom shaped clouds. The area where the explosion occurred in North Korea is believed to contain ballistic missile, and other military facilities. North Korea, like Russia, stores ammunition and military explosives long after it should be disposed of. This stuff degrades with time, but the North Koreans cannot afford to replace aging ammo, so they keep it. And eventually some of it just goes off. It's happened in Russia several times. If North Korea did test a nuclear weapon, they would do it under ground, where the seismographs would pick it up, but there would not be any photo ops above ground.