Federal Reserve Chair Janet Yellen told lawmakers the central bank must press on with monetary stimulus as "significant slack" remains in labor markets and inflation is still below the Fed's goal.

"A high degree of monetary policy accommodation remains appropriate," Yellen said today in semi-annual testimony to the Senate Banking Committee. "Although the economy continues to improve, the recovery is not yet complete."

Yellen cited labor-market weaknesses even after an unexpectedly fast decline in unemployment put pressure on Fed officials to consider accelerating their timetable for an interest-rate increase. Yellen said today that rates are likely to stay low for a "considerable period" after bond purchases end, which she said could happen following the Fed's October meeting.