South Korean stocks plunged Monday following North Korea's announcement that it conducted a nuclear test. The benchmark Korea Composite Stock Price Index, or Kospi, fell as low as 1,303.62, or 3.6 percent after North Korea's official Korean Central News Agency said the underground test was performed successfully. The Kospi was trading 2.9 percent lower at 1,316.57 around 12:50 p.m. (0350 GMT).