The British-based Standard Chartered Bank has been accused of illegally scheming with Iran to launder as much as $250 billion over nearly a decade.
New York prosecutors say the bank hid 60,000 secret transactions for Iranian financial institutions that were subject to United States economic sanctions, as part of a scheme called Project Gazelle.
They have labelled Standard Chartered a rogue institution.
CNN reports that regulators allege the bank actively made the deals then tried to cover them up.
US regulators want to revoke Standard Chartered's US banking licence.
The bank's shares plunged more than 6% in London.