PARIS—Consumer prices in leading industrialized countries fell by 0.3 percent in September over 12 months, the same fall as in August, an organization said Tuesday.

On a monthly comparison of prices, there had been no change in September after a rise of 0.2 percent in August, said the Organization for Economic Cooperation and Development (OECD).

A persistent fall of prices amounts to deflation, which can turn into a vicious cycle of falling prices, falling demand, rising unemployment and a further fall in prices, said the organization.

Part of the purpose of massive support for economies by governments and central banks during the economic crisis, has been to avert deflation and to stimulate activity.

The OECD, a policy forum and research base for the 30 leading industrial economies, also said that prices in the Eurozone fell by 0.3 percent in September after a fall of 0.2 percent in August on a 12-month comparison.

In the United States, prices fell by 1.3 percent in September after a fall of 1.5 percent in August. In Japan prices fell by 2.2 percent in September as in August, the OECD added.