More than 150 American clients of UBS, the Swiss bank, are under criminal investigation as part of a broader crackdown on tax evasion by the US government, according to a court document.

The public confirmation of the initial number of cases under way comes as the US and Swiss governments prepare to reveal the details of an out-of-court settlement over access by the Internal Revenue Service – the US tax authority – to names of up to 52,000 Americans with secret accounts with UBS.