The U.S. blacklisted a Ukrainian billionaire and said it’s ready to help fight corruption in the country at the center of Donald Trump’s first impeachment trial and an effort to discredit President Joe Biden before last year’s election.

Igor Kolomoisky, his wife and his two children are banned from entering the U.S., Secretary of State Antony Blinken said in a statement Friday. While he was governor of Ukraine’s Dnipropetrovsk region in 2014 and 2015, Kolomoisky “was involved in corrupt acts” and used his political influence and power for personal benefit, Blinken said.

“This designation reaffirms the U.S. commitment to supporting political, economic, and justice sector reforms that are key to Ukraine’s Euro-Atlantic path,” Blinken said. “The Department will continue to use authorities like this to promote accountability for corrupt actors in this region and globally.”

The move to penalize Kolomoisky is the first major U.S. initiative on Ukraine under Biden, whose links with the former Soviet nation became a key theme in the 2020 election campaign.

Biden faced criticism from Republicans over efforts to remove a former chief prosecutor, while Trump was impeached for his attempt to make aid conditional on the Ukrainian government announcing an investigation into the then-Democratic candidate and his family.

Kolomoisky, once a business partner and supporter of President Volodymyr Zelenskiy, remains one of Ukraine’s most influential oligarchs. How Zelenskiy deals with him has become a litmus test of his willingness to crack down on corruption that’s dogged the ex-Soviet republic since the fall of communism.

Creditors including the International Monetary Fund have urged Zelenskiy’s administration to recover loses from Kolomoisky, from whom it seized the country’s largest lender Privatbank after discovering a $5.5 billion hole in its finances in 2016.

Kolomoisky and his business partner Gennady Bogolyubov are fighting the government’s legal efforts to recoup the cost of Privatbank’s bailout in several jurisdictions, including the U.S. Both men deny wrongdoing.

At home, prosecutors named three top Privatbank managers as suspects in a fraud investigation last week. Kolomoisky did not immediately respond to messages seeking comments on his being blacklisted by the U.S.

“I also want to express concern about Kolomoisky’s current and ongoing efforts to undermine Ukraine’s democratic processes and institutions, which pose a serious threat to its future,” said Blinken.

This article was provided by Bloomberg News.