Hildebrand has come under pressure following revelations of sensitively timed currency trades by his wife and the sacking of a whistleblower who passed details to the lawyer of a political adversary.

Hildebrand's wife Kashya initiated the sale of 400,000 Swiss francs for $504,000, the auditor PricewaterhouseCoopers said.

"From the email traffic available to us, one can tell that PMH has no knowledge of the initiation of the transaction," it said.

PWC conducts the SNB's annual audit.

(Reporting by Catherine Bosley)