MOSCOW — The United States placed sanctions Friday on a Ukrainian business tycoon seen as the most powerful figure in the country outside of the government, signaling an aggressive new approach by the Biden administration to dealing with corruption in Ukraine.
The businessman, Ihor Kolomoisky, an oil and media magnate, was already under investigation in the United States on accusations of embezzlement and fraud, and of using the proceeds to buy commercial real estate in Cleveland, Ohio.
At home in Ukraine, he is one of the most prominent of the ultrawealthy class of post-Soviet oligarchs and has been both an ally and a political albatross for President Volodymyr Zelensky.
Ukrainian oligarchs exercise outsized influence in the country, controlling the news media and at times financing entire factions in Parliament at odds with American and European efforts to strengthen Ukraine’s pro-Western geopolitical orientation. They have done so even as they kept money in Western banks and investments and sent their children to live or study in Europe and the United States.
The sanctions were announced on Friday by the secretary of state, Antony J. Blinken, and bar Mr. Kolomoisky and members of his family from traveling to the United States because of “involvement in significant acts of corruption.”
The penalty does not have a financial element though some of Mr. Kolomoisky’s assets have already been seized in separate actions by the Justice Department. Mr. Kolomoisky’s portfolio of American real estate has been estimated to be worth several hundred million dollars.
In a statement, Mr. Blinken said Mr. Kolomoisky had used a position in government as a regional governor in Ukraine for his personal benefit. While acknowledging that the Ukrainian holds no official role today, Mr. Blinken said he posed a risk for “ongoing efforts to undermine Ukraine’s democratic processes and institutions,” an apparent reference to his efforts to influence the Zelensky administration. Mr. Zelensky has denied he is beholden to the businessman.
The United States has vacillated for years on how to handle Mr. Kolomoisky, a powerful figure who emerged from the legal and political chaos of the early post-Soviet period in Ukraine.
In the aftermath of the 2014 Ukrainian revolution, Mr. Kolomoisky played a positive role for Ukraine in financing one of the largest and most effective paramilitary units fighting the Russian military intervention, at a time when the regular army was in shambles. Mr. Kolomoisky’s militia, Dnipro, held a section of the battle front west of the city of Donetsk.
But his bank, Privatbank, collapsed in 2016 amid accusations of embezzlement and fraud that Mr. Kolomoisky denies. The bank failure cost the Ukrainian government — and by extension the American and European taxpayers who propped it up with aid funds — about $5.5 billion in a bailout.
The Justice Department has accused Mr. Kolomoisky and business associates of embezzlement and fraud and seized real estate in Cleveland in civil forfeiture actions.
The action on Friday reflected Mr. Biden’s strategy of trying to clean up Ukraine’s internal politics as the best protection against Russian influence.
And it will provide Mr. Zelensky international support for making a clean break with the oligarch, if he so desires. A day before the announcement, Mr. Zelensky’s spokeswoman published an article saying he plans to diminish the role of the oligarchs in Ukraine’s politics.
But that is no simple matter. Mr. Kolomoisky controls a faction in Mr. Zelensky’s political party, the Servant of the People, without which the party would not have a majority in Parliament. Mr. Kolomoisky’s television station supported Mr. Zelensky in the 2019 presidential election.
Handling Ukrainian corruption has been politically tinged in the United States, too.
President Biden has long experience in Ukraine, having handled that portfolio as vice-president in the Obama administration — activities that figured prominently in the first impeachment of President Donald J. Trump.
A central contention of Democratic lawmakers in that trial, in the fall of 2019, was that Mr. Trump had falsely asserted a desire to fight corruption in Ukraine by withholding military aid. In fact, they said, he withheld the aid to pressure Mr. Zelensky to investigate Mr. Biden, at the time a likely opponent in the 2020 presidential election. Mr. Trump’s personal lawyer, Rudolph W. Giuliani, had worked with associates of Mr. Kolomoisky in his efforts to uncover dirt on Mr. Biden in Ukraine.