The financial crisis has left the five biggest banks even more powerful than before, he told an event in Mexico City.

"After the crisis, the five largest banks had a higher concentration of deposits than they did before the crisis," he said. "I am of the belief personally that the power of the five largest banks is too concentrated."

The U.S. Dodd-Frank reform and consumer protection act includes mechanisms for regulators to break up large financial companies, but imposes high hurdles for such action.

"The purpose of Dodd-Frank was to reduce the concentration of power and we have a term called 'too big to fail' ... perversely, these banks are now even bigger, they are too 'bigger' to fail than before."

Last month a group of consumer advocates, academics and economists said they wanted to end "too-big-to-fail" banks, starting with Bank of America Corp.