Standard & Poors Ratings Services said on Tuesday it had slashed U.S. top banks' ratings as part of a process of "applying its new ratings criteria for banks".

The ratings agency said that it had adjusted ratings on 37 of the world's largest financial institutions, including major U.S. banks like Bank of America, Citigroup, Goldman Sachs, Wells Fargo, JPMorgan Chase and Morgan Stanley.

S&P announced newly revised ratings criteria last week after more than a year of study. It said that the changes reflected the agency's new criteria for banks, which assessed risk associated with investment banking, how banks are funded and the role of governments and central banks in industry funding.

Ratings for top British banks like Barclays, HSBC, Lloyds and the Royal Bank of Scotland were also downgraded. Ratings for other European banks including Credit Suisse and Deutsche Bank were unchanged.