Europe's banks, burdened by concerns about exposure to ailing Greece, took a perilous turn on Monday despite efforts by the biggest of them to calm panicked investors.

France's financial system was especially hard hit, with shares in its three largest banks all falling more than 10%, as concerns about Greek default continued to cascade across Europe. European banks are cutting back on dollar-denominated loans, a troublesome sign of credit contraction at a time when American and European economies can least afford it.