Part of the investigation is looking into Citigroup's anti-money laundering policies and systems to prevent financial crimes, the report said.

The Department of Justice, the Federal Bureau of Investigation, and the Internal Revenue Service have been investigating the matter for more than a year.

An investigation focuses on services provided by the bank for a trust that held the sanctioned billionaire’s assets.

Citigroup (NYSE:C) is under investigation by the Department of Justice, the Federal Bureau of Investigation, and the Internal Revenue Service for its alleged involvement with a trust that holds assets tied to Suleiman Abusaidovich Kerimov,