The Federal Reserve said it will buy $45 billion a month of Treasury securities starting in January, expanding its asset-purchase program, and it linked the outlook for its main interest rate to unemployment and inflation.

"The committee remains concerned that, without sufficient policy accommodation, economic growth might not be strong enough to generate sustained improvement in labor-market conditions," the Federal Open Market Committee said today at the conclusion of a two-day meeting in Washington.

The Fed said interest rates will stay low "at least as long" as the unemployment rate remains above 6.5 percent and if inflation "between one and two years ahead" is projected to be no more than 2.5 percent. The committee "views these thresholds as consistent with its earlier date-based guidance."