Citigroup is being investigated by several US agencies for the work it has done for a trust that holds the assets of Suleiman Abusaidovich Kerimov, a Russian official sanctioned by the US government, as federal officials continue to scrutinise how Russia’s oligarchs store and access their assets abroad. 

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