Seoul stocks opened sharply lower Thursday, as concerns over the sustainability of artificial intelligence and hotter-than-expected inflation in the United States dampened investor sentiment. After opening sharply lower, the benchmark Korea Composite Stock Price Index tumbled 348.47 points, or 5.8 percent, to 5,660.34 as of 9:15 a.m. The sharp drop in the index triggered the country's bourse operator to issue a sell-side sidecar soon after the market opened.