Zurich prosecutor Andreas Ochsenbein told the Sonntag newspaper his office had been in touch with UBS officials.

'There have been a few individual discussions, which, however, were not interrogations, either in form or content,' he was quoted as saying.

'The prosecution for economic crimes observes with great attention the development in connection with the subprime crisis since last autumn. In that respect, the publically available information is being examined.' Switzerland's biggest bank has made more writedowns than any other European bank in the crisis triggered by the collapsing U.S. mortgage market.

The Sonntag newspaper said the prosecutors were investigating whether UBS management had failed to fully inform or had misled investors with their comments during the crisis as well as whether the business was properly run.

Zurich prosecutors were not available for comment on the report and a UBS spokesman declined to comment.

Separately, the SonntagsZeitung said Zurich prosecutors had been in touch with the Swiss banking regulator last week to obtain a report into the causes of the crisis at UBS.

The newspaper said the prosecutors only expected to make an initial assessment of the document in a week and would then decide whether to open a formal criminal investigation.

Earlier this month, UBS agreed with the Swiss government on a package to shore up its finances, including raising 6 billion Swiss francs in new capital and transferring $60 billion of toxic assets into a new fund controlled by the central bank. -- THOMSON REUTERS