"The last few days highlight once again how important (is) a more and better regulated environment for ratings," the economic affairs commissioner, Olli Rehn, and the commissioner in charge of financial services, Michel Barnier, said in a joint statement.

"Our services are now working as quickly as possible" on a package of reform proposals, the statement said, adding that the package was "due before the end of the summer."

Ratings agency Moody's on Monday slashed Greece's credit rating by three notches from Ba1 to B1 and struck again on Thursday, demoting Spain by a notch to Aa2.

The ratings moves come ahead a summit by eurozone leaders on Friday to thrash out the details of a bailout fund to be set up from 2013 to deal with any potential future crises like that seen in Greece.