U.S. warned of possible downgrade (ext)

NEW YORK (CNNMoney) -- Quit messing around.

U.S. lawmakers got another stern warning from a leading credit rating agency on Thursday that there is now a very real possibility that the country's top-notch credit rating could be downgraded in the next three months.

Standard & Poors said in a statement it was placing the United States' sovereign rating on "CreditWatch with negative implications."

"[O]wing to the dynamics of the political debate on the debt ceiling, there is at least a one-in-two likelihood that we could lower the long-term rating on the U.S. within the next 90 days," the agency said in a statement.

The action on Thursday follows a move in April when S&P changed its outlook on the U.S. AAA rating to "negative" because at the time it couldn't see how lawmakers would create a path to real debt reduction.

Since then "the political debate about the U.S.' fiscal stance and the related issue of the U.S. government debt ceiling has, in our view, only become more entangled," the agency said.

"[W]e believe there is an increasing risk of a substantial policy stalemate enduring beyond any near-term agreement to raise the debt ceiling," S&P noted.

A downgrade of U.S. credit would mean interest rates on U.S. bonds would go up. And it could have ramifications across global markets because U.S. bonds are considered the world's safe haven investment.