GENEVA, SWITZERLAND - SWISS bank UBS will be forced to reveal the names of rich American clients who may have used its services to avoid paying income taxes, according to a report published on Thursday in the Wall Street Journal.

UBS declined comment when contacted on Thursday.

According to the report, US prosecutors will use a subpoena to make the bank reveal its client list, after an indictment in the Florida federal court on Tuesday of former UBS private banker Mr Bradley Birkenfeld and Liechtenstein businessman Mr Mario Staggl.

Last week, the Swiss bank made a securities filing revealing the Justice Department's probe into its activities.

'In particular, DOJ is examining whether certain US clients sought, with the assistance of UBS client advisors, to evade their US tax obligations by avoiding restrictions on their securities investments,' the Swiss bank's securities filing said.

Mr Banks often help wealthy clients to legally minimise their tax bills, but it is illegal in the US actively to evade paying income tax on earnings.

The probe of UBS comes after US tax authorities opened an investigation of over 100 Americans in late February related to bank accounts held in the secretive European principality of Liechtenstein.

UBS had also revealed earlier that one of its top executives had been detained in the US as part of the tax-related probe.

The bank said the executive would remain in the US pending 'discussions' with the US authorities. UBS said it had been told that the executive, who it did not identify, was regarded as a 'witness' in the case.

The Financial Times newspaper has named the detained executive as Mr Martin Liechti, a Zurich-based executive who runs part of UBS's international wealth management business.

The newspaper said Mr Liechti - who was also Mr Birkenfeld's former boss - was detained in the US state of Florida late last month.

UBS' filing said the tax investigation was linked to services its advisors had provided American clients between 2000 and 2007. -- AFP