The Justice Department is investigating whether the Standard & Poor's credit ratings agency improperly rated dozens of mortgage securities in the years leading up to the financial crisis, The New York Times reported Wednesday.

The investigation began before Standard & Poor's cut the United States' AAA credit rating this month, but it's likely to add to the political firestorm created by the downgrade, the newspaper said. Some government officials have since questioned the agency's secretive process, its credibility and the competence of its analysts, claiming to have found an error in its debt calculations.

The Times cites two people interviewed by the government and another briefed on such interviews as its sources. According to people with knowledge of the interviews, the Justice Department has been asking about instances in which the company's analysts wanted to award lower ratings on mortgage bonds but may have been overruled by other S&P business managers.

If the government finds enough evidence to support a case, it could undercut S&P's longstanding claim that its analysts act independently from business concerns. The newspaper said it was unclear whether the Justice Department investigation involves the other two major ratings agencies, Moody's and Fitch, or only S&P.