UBS has confirmed it is being investigated by US authorities into whether it helped Americans evade taxes through investments banned in the US.
The Swiss bank said US regulators were investigating potential sales of so called “bearer bonds”.
These bonds can be transferred without registering ownership, enabling wealthy clients to potentially hide assets.
“We are cooperating with the authorities in these investigations,” the bank said.
The fresh investigation by the US Attorney’s Office for the Eastern District of New York and from the US Securities and Exchange Commission comes after UBS paid $780m (£512m) in 2009 to settle a separate Justice Department tax-evasion probe.