In a statement, the U.S. Treasury Department said it had blacklisted Ukrainian parliamentarian Andriy Derkach, who it accused of being "an active Russian agent for over a decade," using "manipulation and deceit" in his effort to influence elections in the United States and around the world.
Derkach's name has repeatedly come up in connection with unsubstantiated allegations by President Donald Trump, his personal lawyer, Rudy Giuliani, and some Republican lawmakers that Hunter Biden used his influence with his father to help Burisma, an energy company on whose board he sat, and that Joe Biden pressured Ukraine to fire a top prosecutor who had investigated the firm.
Derkach did not immediately return a message seeking comment, but told Politico in July it was "nonsense" that he is trying to interfere in the U.S. election.
Democrats allege that Derkach has helped orchestrate the Biden allegations. They and others have expressed particular alarm over Derkach's ties to Giuliani, as well as the Ukrainian's boasts about feeding material to U.S. legislators.
Derkach has previously disseminated information about Hunter Biden and Burisma that Giuliani has cited as evidence in his criticisms of the Biden family.
Giuliani did not immediately respond to a request for comment, but the former New York mayor has told the Washington Post that he has had frequent contacts with Derkach. The pair met in December during a trip to Ukraine as part of an effort by Trump's allies to obtain damaging information about Biden.
Derkach also told Politico earlier this year that he notified Republican and Democratic lawmakers about materials he has published and aired at his news conferences. Among them was Republican Senator Ron Johnson, who is overseeing an investigation of the Bidens as chairman of the Senate Homeland Security and Governmental Affairs Committee, he said.
A message left with Johnson's office was not immediately returned. Johnson has denied receiving any information from Derkach and rejected Democratic allegations that his investigation is being fueled by Russian disinformation.
The Treasury's move on Thursday also targeted three Russian nationals that it said were employees of Russia's Internet Research Agency (IRA), which was indicted by former U.S. Special Counsel Robert Mueller as part of his probe into alleged Russian interference in the 2016 U.S. election.
One of the employees, Artem Lifshits, was separately charged by the U.S. Justice Department in a conspiracy to use stolen identities of Americans as part of an operation to "disrupt the democratic process and spread distrust towards candidates for political office."
"The United States will continue to use all the tools at its disposal to counter these Russian disinformation campaigns and uphold the integrity of our election system," Treasury Secretary Steven Mnuchin said in Thursday's statement.
Treasury's measures freeze any U.S. assets of those blacklisted and generally bar Americans from dealing with them.