Amadeu Altafaj, a spokesman for the European Commission, said the report in the Spanish newspaper El Economista was "very bizarre" and added: "I can firmly deny it."

An IMF spokeswoman said it was "totally unfounded".

But market worries about Spain's debt position continued to simmer, with the yield spread on Spanish/German 10-year bonds rising to a euro lifetime high of 223 basis points.

"The noise surrounding some form of backstop facility for Spain has increased dramatically," said Silvio Peruzzo, an economist at RBS in London.

A 440 billion-euro ($543 billion) special-purpose vehicle (SPV) is already in place for any euro zone country that runs into Greek-style payment problems, finalized earlier this month by ministers from the 16 countries that use the single currency.

The newspaper report, citing sources "close to the issuing entity", said a liquidity plan specifically aimed at Spain had been discussed by IMF board directors and was aimed at staving off a rescue similar to that offered to debt-laden Greece.