Federal Reserve Chairman Jerome Powell signaled that the central bank would pull out the stops to combat a global disinflationary downdraft, foreshadowing a potential shift toward an easier monetary policy over time.

Speaking to reporters on Wednesday, after the Fed left its benchmark interest rate unchanged, Powell said he is intent on evading the downward spiral in inflation and inflation expectations that's bedeviled other countries.

"We have seen this dynamic play out in other economies around the world, and we are determined to avoid it here in the U.S.," he said. The strong words—combined with a minor yet telling tweak in the Fed's post-meeting statement—suggested that the central bank is moving toward a major change in how it interprets its price-stability mandate as it completes a review of its policy framework by midyear.