Moody’s Corp. is being investigated by Italian prosecutors for alleged market manipulation related to a report on the country’s banks published in May.

“Moody’s takes its responsibilities surrounding the dissemination of market-sensitive information very seriously,” the company said in an e-mailed statement today. The ratings firm also said it’s cooperating with the inquiry.

Moody’s on May 6 said in a report it was assessing the risk of “sovereign contagion” that could affect the banking industries of Portugal, Spain, Italy, Ireland and the U.K. Italy isn’t among the countries most at risk from Europe’s spreading debt crisis and its credit outlook for 2010 remains stable, Moody’s said the following day.

Stocks and bonds dropped throughout Europe on May 6 amid market rumors, later denied, that ratings firms were set to downgrade the sovereign debt of several southern European countries. Italian market regulator Consob said on May 7 it was reviewing trading in bonds and stocks for possible “irregularities” after the benchmark FTSE MIB Index tumbled as much as 6.3 percent the previous day before paring losses.

The review is still ongoing, a Consob official said today.

The Moody’s probe was reported earlier in La Repubblica newspaper.