The Nikkei stock index briefly dropped over 3 percent Thursday afternoon, trading at its lowest intraday level in about 14 months, as selling accelerated on growing concern that the U.S. Federal Reserve may raise interest rates faster than expected. As of 12:45 p.m., the 225-issue Nikkei Stock Average was down 888.58 points, or 3.29 percent, from Wednesday to 26,122.75. The broader Topix index of all First Section issues on the Tokyo Stock Exchange was 54.03 points, or 2.86 percent, lower at 1,837.82.