From the article:
North Korea announced Monday that it conducted another nuclear test, a surprise move certain to further isolate Kim Jong-il's increasingly unpredictable regime.
News of the test, the second conducted by North Korea, came in a statement by the official Korean Central News Agency. "According to the demand of our scientists and technicians, our republic has successfully conducted another underground nuclear test on May 25
North Korea warned last month that it would conduct another nuclear test, allegedly to protest a rather mild rebuke from the United Nations Security Council following an April 5 "satellite launch" by Pyongyang that the United States, South Korea and Japan interpreted as a camouflaged test of its ballistic missile system..