The U.S. Justice Department has said Maria Butina, accused of operating as a Russian agent, was working at the direction of an unnamed senior official at the Russian central bank.

The Russian Central Bank said on Friday that Deputy Governor Alexander Torshin, who is on a U.S. sanctions blacklist and has been tied to an investigation into a suspected Russian agent operating in Washington, is leaving the bank to retire.

A person familiar with the matter told Reuters that Butina worked as an assistant for Torshin. Butina's lawyers have identified Torshin as the person with whom she was accused of working.

Torshin has not replied to requests for comment on the U.S. investigation. The Russian central bank declined additional comments when contacted by Reuters on Friday.

Torshin, who turned 65 on Tuesday, was hit by U.S. sanctions in April along with a number of Russian businessmen and government officials seen as close to President Vladimir Putin.

The U.S. Treasury Department said the measures were a response to what is described as Russia's malign activity, including its actions in Ukraine, its support of President Bashar Assad in Syria's civil war and subverting Western democracies.

Butina is accused of working with a Russian official and two unidentified U.S. citizens to try to infiltrate a U.S. gun-rights organisation and influence American foreign policy toward Russia. Moscow has called the case against Butina fabricated and demanded her release.