The Federal Reserve on Wednesday left its key interest rate near zero but signaled it remains on course to raise interest rates in September or later this year, citing progress in the U.S. job market. The Fed said that, although the labor market had improved, there is lingering concern about low inflation. Central to the Fed’s thinking is how it perceives its progress in achieving its “dual mandate” of maximum employment and inflation near 2 percent. The Fed has said it will raise rates when it has seen improvement in the job market and becomes “reasonably confident” inflation is on course to return to 2 percent. The benchmark federal funds rate has been near zero since December 2008, or 2,417 straight days. The central bank has three scheduled policy meetings left to change the rate, Sept. 16-17 being the next one.