WASHINGTON, July 30 -- The Dow Jones Industrial Average posted its worst session in fifteen months Wednesday, shedding 1,129 points after the Federal Reserve held interest rates steady for a seventh consecutive meeting and revealed a policymaking committee more fractured on inflation than markets had anticipated.

The Federal Open Market Committee voted 9 to 3 to leave the federal funds rate in its 3.50 to 3.75 percent range. Beth Hammack of the Federal Reserve Bank of Cleveland, Neel Kashkari of Minneapolis, and Lorie Logan of Dallas all voted against the majority, formally preferring a quarter-percentage-point increase. Their simultaneous dissents represent the sharpest internal division the committee has produced in years.

The Dow Jon...