Barron’s cited a source close to the matter, who claimed the US Department of Justice, the Federal Bureau of Investigation, and the Internal Revenue Service have been investigating for over a year. This mainly centres around services the bank provided to Heritage Trust, which Barron’s reports holds assets of Kerimov.

A Citi spokesperson said: "Citi is committed to conducting all business with the highest consideration for compliance with all applicable laws and regulations. At the same time, we are actively ending nearly all of our institutional banking business in Russia, except for those operations necessary to fulfil remaining legal and regulatory obligations, while we proceed with the closing of our Russian consumer banking business."

Barron’s also reported the probe is looking at Citi’s compliance frame workwork, including anti-money-laundering and client-vetting processes.