In an annual filing with securities regulators on Friday, Citigroup said it had received a subpoena from the U.S. Attorney for the Eastern District of New York asking about banking relationships and transactions at its Citibank unit by "certain individuals" said to be involved in the alleged wrongdoing.

The company said it is cooperating with the investigation. A spokesman declined to comment further.

(Reporting by David Henry in New York; Editing by Lisa Shumaker)