The announcement by Moody's Investors Service today that it has downgraded the credit rating of two of France's largest banks revived concerns that Europe's lingering sovereign-debt crisis threatens the region's top financial institutions.

In a widely anticipated decision, Moody's lowered the long-term debt rating of Societe Generale and Crédit Agricole, citing funding and liquidity problems for SocGen and Greek exposure for Crédit Agricole. The ratings firm kept BNP Paribas unchanged, though maintained it under review.