NEW YORK, Feb 20 (Reuters) - The S&P 500 posted its worst daily percentage decline since mid-November on Wednesday after minutes from the U.S. Federal Reserve suggested the central bank may slow or stop buying assets sooner than expected.

Based on the latest available data, the Dow Jones industrial average was down 108.13 points, or 0.77 percent, to end unofficially at 13,927.54. The Standard & Poor's 500 Index was down 18.99 points, or 1.24 percent, at 1,511.95. The Nasdaq Composite Index was down 49.19 points, or 1.53 percent, at 3,164.41. (Reporting by Caroline Valetkevitch; Editing by Jan Paschal)