Federal Reserve policymakers are open to further efforts to stimulate the U.S. economy if growth falters or threats escalate.

Minutes of the central bank's April 24-25 meeting stated that "several members" thought additional Fed support could be needed if the recovery lost momentum or if the risks to the economy became great enough. The minutes did not spell out such circumstances.

The comments stood in contrast to the previous minutes, which said only "a couple" of members expressed support for further bond purchases, the most dramatic move the Fed has left to boost the economy.

The Fed also announced that for the rest of this year and next year all of its meetings will last for two days, to allow more time for discussion.