"A separation or a sale of investment banking, as is sometimes demanded, would be senseless for our business and our customers," Chairman Urs Rohner told the Neue Zuercher Zeitung newspaper in an interview.

"It's much more about optimizing the business model and better balancing it with regard to capital allocation."

The bank unveiled measures on Wednesday to boost its capital base in response to criticism from the central bank, and also announced new cost cuts, including at the investment bank, although some analysts have called for even more radical steps.

Rohner said the main mistake the bank had made was to be too upbeat about the economy after the financial crisis of 2008.

"In retrospect, it was wrong that we were too optimistic after the recovery in 2009 and built up too much capacity, mostly in investment banking but also in private banking. That cost money," he said.

He reiterated comments made in a separate interview published on Friday supporting Chief Executive Brady Dougan, who had come under heavy fire after the central bank attack.

"With Brady Dougan we have a CEO who knows the business better than any other CEO who I know," he said.

"What is important is that Brady Dougan has a vision of how to lead the company and knows how to motivate 50,000 employees at a time of upheaval."

(Reporting by Emma Thomasson, editing by William Hardy)

• A Permanent Economic Emergency