Martin Winn, an S&P spokesman in London, didn't immediately reply to a request for additional comment after forwarding the rating notes.

French Finance Minister Francois Baroin asked market regulators in France and Europe to investigate the "causes and potential consequences" of S&P's erroneous message.

"S&P denied the rumor and confirmed the French rating, but this had consequences," he said at a conference in Lyon.

France's stock-market regulator subsequently opened an investigation into S&P's dissemination of the erroneous message.

"It clearly raises issues about internal systems and controls," said Christopher Whalen, managing director of Institutional Risk Analytics, a Torrance, California-based bank- rating firm. "The onus is on them to be careful and it's troubling. Whether you're a broker dealer or a rating agency, everything you say has to be very carefully considered because of the weight that they carry."

S&P downgraded the U.S.'s AAA credit rating by one level to AA+ for the first time Aug. 6, citing the nation's political process and criticizing lawmakers for failing to cut spending or raise revenue enough to reduce record budget deficits.

The New York-based rating company's decision was flawed by a $2 trillion error, according to the Treasury Department. S&P disputed the Treasury's assertions and said using the department's preferred spending measures in its analysis didn't affect its credit grade.

So far, the EFSF has sold two five-year bonds and one 10- year security, all in the first half of this year, and it may have to finance more than 70 billion euros ($95 billion) of a planned second aid package for Greece. European leaders last month agreed to boost the rescue fund to 1 trillion euros from 440 billion euros.

Volatility in financial markets has increased since July on speculation Europe's debt crisis will spread to larger countries such as Italy. The Mediterranean nation, the world's eighth- biggest economy, saw the yield on its 10-year bond jump above 7 percent yesterday as leaders rush to approve debt-reduction measures. Greece, Portugal and Ireland each sought bailouts after their bond yields traded above 7 percent.

The Chicago Board Options Exchange Volatility Index, or Vix, as the benchmark measure of U.S. equity derivatives is known, jumped 32 percent yesterday to 36.16, the highest since Nov. 1.