And French banks BNP Paribas and Credit Agricole both revealed they are carrying out internal probes into potential breaches of US regulations – although they would not say whether or not this is related to sanctions against Iran.
UniCredit is being investigated by the US Treasury’s office of foreign assets control, the Justice Department and the New York County district attorney’s office.
Its German unit HBV is accused of breaking rules over trade and transactions with Iran.
The revelations come in the same month as UK-based developing markets specialist Standard Chartered paid $340m (£215.2m) to the New York state department of financial services to settle charges over sanction-breaking.
Separately US authorities are investigating RBS and Germany’s Commerzbank, while HSBC has been accused of inadvertently enabling money laundering with its lax controls in countries including Mexico, Syria and Iran.