A major international economic organization is warning that developed countries have slowed efforts to reform their economies since the aftermath of the world financial crisis.

The Organization for Economic Co-operation and Development, a think tank dealing with the world's developed countries, says in a report that the lagging attention to reform is preventing many advanced economies from returning to the growth rates they enjoyed before the crisis.

The report was released as finance ministers and central bankers from the Group of 20 wealthy and developing nations began a two-day meeting in Istanbul. In a statement accompanying Monday's report, the OECD's chief economist, Catherine Mann warns of a "protracted period of stagnation" in some advanced economies.

The statement noted "growing difficulties by governments in pushing for reforms."