The IMF is urging the ECB to expand its balance sheet as part of a multitrillion-dollar effort to tame the euro-zone debt crisis.
The IMF's comments, made to the Group of 20 largest industrialized and developing economies, is a controversial call for stronger ECB intervention than the IMF has previously made public.
The IMF has said the ECB's role has been essential in preventing a cascade of defaults and bank failures. It has said the central bank should continue its crisis-fighting efforts of providing cheap cash to the banking system and buying the bonds of ailing euro-zone countries to keep borrowing costs down until leadership is able to boost the size of its bailout facilities.
But now, it appears the IMF fears that may not be enough.