"I am responsible for everything that happens in the bank. But if you ask me if I feel guilty, then I would say no," Oswald Gruebel, chief executive of the bank, told Swiss newspaper Sonntag in an interview published Sunday.

When someone is driven by criminal intent, "you can't do anything," said Gruebel.

The chief executive also shrugged off Socialist calls for his resignation as "all political."

"I am not thinking about resigning," he added, pointing out that this would be a question for the management board.

Gruebel, a German who was previously at the helm of Credit Suisse, took over the reins of UBS at the height of the financial crisis when the bank was struggling to recover after losing billions of francs and turning to state aid.

He helped to steer the ailing bank from record losses back to profit in 2010.

But pressure has been mounting on Gruebel and the head of investment bank Carsten Kengeter since the unauthorised trades were uncovered on Thursday.

The bank's honorary chairman Nikolaus Senn told Swiss German television late Friday that he doubted that Gruebel could stay after the debacle.

Senn said that adequate checks were not implemented and criticised Gruebel for his over-reliance on the controls system to uncover problems.

"I don't know how many times Oswald Gruebel flew to London in order to understand from the managers on site what was going on," Senn said.

In London, equities trader Kweku Adoboli, 31, was charged Friday with fraud and false accounting.

The bank announced the massive loss through unauthorised trading just hours after the trader was arrested at UBS's London offices at 3:30 am (0230 GMT) on Thursday.

Copyright AFP (Agence France-Presse), 2011