Andreas Albrecht, chairman of the supervisory board of Basler Kantonalbank, said in an interview with Basler Zeitung, and seen by Family Wealth Report, that his bank opened accounts for thousands of UBS customers after the US tax probe against the Zurich banking giant.

"It was mainly Swiss customers, but also a lot of foreigners, including of course Americans," Albrecht said.

"Looking back, I have to say it would have been wiser to close the door sooner for Americans, who only made up a marginal share of our business," he said, adding that the bank stopped accepting US-based clients in March 2009.

In August, the US Justice Department identified Basler Kantonalbank in an indictment against a Swiss banker accused of helping US citizens move their money away from UBS.

Switzerland’s historic bank secrecy laws were partially breached in 2009 when US and Swiss authorities agreed that UBS should hand over details on 4,450 client accounts to the US to settle civil claims of it helping wealthy US citizens to dodge taxes. Earlier in 2009, in a separate, criminal case, UBS agreed to pay $780 million to settle charges of aiding tax evaders. Since then, a number of Swiss banks, such as Julius Baer and Wegelin have ceased to provide offshore banking to US clients.

Once the crackdown was launched on UBS, it raised the question of what some clients or potential clients would do in taking their money elsewhere.

In the Basler Kantonalbank case, Martin Lack, a former UBS banker turned independent asset manager, has been charged with conspiracy to defraud the United States by helping US customers "open and maintain secret bank accounts at a Swiss cantonal bank headquartered in Basel, Switzerland, with the assistance of a private banker at the bank," the Justice Department said. The bank itself hasn't been charged with any crime.

Albrecht told the newspaper that his bank did not violate Swiss laws, but had worked on the assumption that some of its clients' deposits hadn't been declared to tax authorities.