The Federal Reserve on Wednesday left in place its monthly $85 billion bond-buying stimulus plan, arguing the support was needed to lower unemployment even as it indicated a recent stall in U.S. economic growth was likely temporary.

The U.S. central bank predicted that the nation's job market would continue to improve at a modest pace, and repeated a pledge to keep purchasing securities until the outlook for employment "improves substantially."

"Growth in economic activity paused in recent months, in large part because of weather-related disruptions and other transitory factors," the Fed said after a two-day meeting.

A report on Wednesday showed the U.S. economy unexpectedly contracted in the fourth quarter as inventory investment slowed and government spending plunged. Analysts said superstorm Sandy, which slammed into a large swath of the U.S. East Coast in late October, also disrupted the recovery.