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

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

Citigroup is being probed by U.S. government agencies over its ties to sanctioned Russian billionaire Suleiman Abusaidovich Kerimov, Barron's reported on Thursday, citing a person familiar with the matter.

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