MarketWatch.com Story The news triggered an emergency security meeting among South Korea officials and forced a temporary halt to trading on South Korea's main stock market. News reports cited North Korea's state-run Korean Central News Agency as saying the nation had "successfully conducted another underground nuclear test on May 25 as part of its measures aimed at strengthening its self-defense nuclear deterrent in every way." South Korean officials said earlier that it suspected a nuclear test had taken place after detecting an "artificial earthquake." The U.S. Geological Survey reported an earthquake of magnitude of 4.7 on the Richter scale, centered about 230 miles northeast of Pyongyang. The epicenter is in the same area where North Korea conducted its previous nuclear test in October 2006. Trading on the South Korean stock market was halted briefly after shares fell sharply in the wake of the news. Stocks recouped some of those earlier losses to trade 2.5% lower by late morning. Japan's Nikkei index was 0.9% higher at 9,307.03. North Korea's state media made the announcement around noon local time, or about two hours after South Korean officials detected the unusual seismic activity. Pyongyang said in late April it would conduct more tests of nuclear devices and missiles. South Korea's President Lee Myung-bak had called an emergency security meeting to assess the situation, Yonhap reported. US condemns North Korea missile test - Telegraph Facing his first major foreign policy test since taking office in January, President Barack Obama accused Pyongyang of threatening the security of nations "near and far" and called for a "new approach" to addressing the threat of nuclear proliferation. "This provocation underscores the need for action not just at the UN Security Council, but in our determination to prevent the spread of these weapons," he said, before talks with European leaders in Prague. What will be Obama's reaction this time around? What message is this sending to other potential nuclear players such as Iran?