Looking at the longer term, Moody's said the countries face...

Looking at the longer term, Moody's said the countries face "dramatic increases" arising from aging-related pension and health care subsidies. "These future costs must be brought under control if these countries are to maintain long-term stability in their debt burden credit metrics," the Moody's report said.

Sirou's comments in Paris were not based on any new information, and simply built on previous Standard & Poor's reports, said spokesman David Wargin.

An S&P report in 2009 said "fiscal risk has noticeably increased," for the United States as it has taken on more debt to stimulate the economy. But Standard and Poor's maintained its AAA rating on US debt with a "stable" outlook because other factors outweigh the risks, the report said.

While US debt is high, the Treasury has a special advantage in paying off loans because the dollar remains the world's global reserve currency, Hess said." That means the United States is in the unique position of being able to print its own dollars to pay off its debt".