The St Gallen-based bank, Switzerland's oldest, said the decision had been taken in response to stricter measures introduced in the US against tax dodgers and planned changes to estate tax, which would make some non-US citizens liable to tax if they inherited US securities.
In a letter to investors it said Swiss banks were likely to find themselves in an untenable position, as they would be expected to know which clients were liable to pay US tax – "an impossible undertaking", given the lack of clear definitions in the matter.
The danger of inadvertently making false declarations to the US tax authorities will be too great, it explained.
It added that it believes the US overestimates its attraction as a financial centre, and is advising its clients to get out of all US securities.
The decision comes a week after US tax authorities reached a deal with the Swiss government which will see bank UBS hand over details of almost 4,500 suspected tax cheats.