The Commission's plans to give the ECB the power to oversee all banks is intended as a first step towards a full European banking union. The EU executive body is due to publish its detailed proposals on banking supervision on September 12.

"The ECB has itself said it does not have the potential to supervise the European Union's 6,000 banks in the foreseeable future," Schaeuble told German radio, expressing scepticism about the timeframe envisaged in the Commission proposals.

"I have doubts that this (banking supervision) can come so fast," he said, adding that a distinction should be drawn between smaller banks and systemically relevant institutions.

"With the bigger, systemically relevant banks there is a chance that direct supervision by the ECB could be realised in a foreseeable period of time," Schaeuble said.

EU Commissioner Michel Barnier's plan would rob national supervisers of much of their authority, leaving them with routine tasks such as consumer protection. But euro zone countries must approve the proposal before it becomes law.

Schaeuble said euro zone finance ministers might consider the Commission proposals on Sept. 15.

Despite the presence of some 6,000 banks in the European Union, the vast majority are small and relatively insignificant and more than 90 percent of all assets are held by only around 200 institutions, analysts say.

Schaeuble did not make clear which institutions he would consider to be 'systemically important'. The 200 would include the larger German state-owned Landesbanks and Spanish 'cajas' where many of the European banking sector's woes originate.

Berlin is keen to keep its state-owned Landesbanks, with their cosy relationships with politicians and businesses, out of the supervisory clutches of the ECB.