An accelerating flight of deposits from banks in four European countries is jeopardizing the renewal of economic growth and undermining a main tenet of the common currency: an integrated financial system.

A total of 326 billion euros ($425 billion) was pulled from banks in Spain, Portugal, Ireland and Greece in the 12 months ended July 31, according to data compiled by Bloomberg. The plight of Irish and Greek lenders, which were bleeding cash in 2010, spread to Spain and Portugal last year.

The flight of deposits from the four countries coincides with an increase of about 300 billion euros at lenders in seven nations considered the core of the euro zone, including Germany and France, almost matching the outflow. That's leading to a fragmentation of credit and a two-tiered banking system blocking economic recovery and blunting European Central Bank policy in the third year of a sovereign-debt crisis.