Barclays' private bank in Switzerland has dropped out of a U.S. program aimed at cracking down on wealthy Americans evading taxes through hidden offshore accounts, the British bank's market head for Switzerland said on Thursday.

"We have recently exited the program," Barclays executive Francesco Grosoli said at an event in Zurich, adding that the bank had done so "three or four months ago" after evaluating its options and seeking advice. Grosoli did not elaborate.

A host of Swiss banks have come forward to join the program, which requires them to hand out some previously hidden information and potentially face penalties of up to 50 percent of assets they managed on behalf of U.S. clients.