S&P cut the long-term U.S. credit rating by one notch to AA-plus. The credit agency said it was making the move because the deficit reduction plan passed by Congress Tuesday did not go far enough to stabilize the country's debt situation.
U.S. Treasury securities, once undisputedly the safest investment in the world, are now rated lower than bonds issued by countries such as the United Kingdom, Germany, France or Canada.
The move is likely to raise borrowing costs eventually for the American government, companies and consumers.
"The downgrade reflects our opinion that the fiscal consolidation plan that Congress and the administration recently agreed to falls short of what, in our view, would be necessary to stabilize the government's medium-term debt dynamics," S&P said in a statement issued late Friday, after financial markets were closed for the week.