The rare decision came after the introduction of new European guidelines that allow regulators to question agency moves, said the spokesman.

Standard and Poor's on Friday warned that attempts by Italy to correct its public finances faced "risks", a day after the government's adoption of a 47-billion-euro austerity plan.

And Moody's has said it had put the ratings of 16 leading Italian banks on review for a possible downgrade.

S and P were asked to explain itself on Monday while Moody's was to follow suit a couple of days later.

The Consob focused on S and P as it had published its opinion before a decision by Prime Minister Silvio Berlusconi's government on its austerity programme had become official.

This means that the US agency based itself "on press leaks, which does not seem to be a very precise working method", said a source close to the securities market regulator.

The Consob is also trying to understand why the opinion was published at 1100 GMT when markets were still open as it risked having an impact on market trends.

The regulator asked ratings agencies last year to publish their outlook after markets have closed.

Moody's believes that the Consob request of an explanation is linked to market anomalies the day after the agency published its warning with Unicredit plunging more than eight percent.

The regulator also asked ESMA, the independent EU authority that contributes to safeguarding the stability of the European Union's financial system, to look into the issue at a meeting in Paris next week.

Copyright AFP (Agence France-Presse), 2011