Rudy Giuliani didn’t just push the Ukrainian government to announce investigations that would boost President Donald Trump’s political prospects. The former New York mayor—who is not part of the U.S. government—also raised concerns to Ukrainian officials about a senior aide to President Volodymyr Zelensky, according to American and Ukrainian sources familiar with his comments.

That aide, Andriy Bohdan, previously worked for an oligarch who had sparred with Giuliani’s then-allies Lev Parnas and Igor Fruman. Giuliani’s comments led Ukrainian officials to believe he was pushing for the aide’s ouster. A Zelensky administration official familiar with the discussions said he was not aware of Giuliani explicitly requesting Bohdan’s removal.

Giuliani’s communications with Ukrainian government officials and efforts to influence their decisions are at the heart of Democrats’ impeachment inquiry. Giuliani has refused to cooperate with both Democratic and Republican members of Congress seeking more information about his work as Trump’s unofficial Ukraine czar. While he was undertaking that project at Turmp’s behest, Giuliani also had talks with Ukraine’s top prosecutor about representing him, according to The Washington Post.

Reached for comment, Giuliani did not dispute this reporting.

“[A]lmost everyone me I spoke to about Boldan [sic] including Ambassador Volker described him [as] a very crooked lawyer,” he wrote in an email. “There’s really not much dispute.”

Kurt Volker, formerly the U.S. special envoy to Ukraine, declined to comment on Giuliani’s statement.

Giuliani says he has not traveled to Ukraine since he began investigating a natural gas company where Hunter Biden was a board member. But he has had communications with people close to Zelensky, including aide Andriy Yermak.

State Department officials were also concerned about Bohdan, according to people familiar with their thinking, specifically his longtime association with oligarch Ihor Kolomoisky.

Bohdan represented Kolomoisky in litigation over the future of PrivatBank, a bank he previously controlled and which the government of Ukraine subsequently nationalized. Ukrainian officials have alleged that Kolomoisky stole billions of dollars from the bank. The FBI has also scrutinized the billionaire for possible financial crimes involving the bank, as The Daily Beast and Bloomberg have reported.

And Yermak, who was in touch with Giuliani, said any effort to push Zelensky to fire an aide would have failed.

“The question itself is incorrect,” he said in a statement. “No one can put pressure on President Zelensky in that way.”

A former U.S. official familiar with the matter said American officials discussed concerns about Bohdan privately, and decided not to specifically name him in official talks with Zelensky’s aides.

“We were aware of the relationships and assertions about him, but it could also be argued that he could be just what Zelensky needed—someone who knows the system,” the former U.S. official said. “So we decided that we would trust Zelensky and expect him to be true to his pledges on corruption and reform.”

Kolomoisky had a run-in with Parnas and Fruman earlier this year, when the pair traveled to Tel Aviv to meet with him.

It came before Zelensky’s inauguration. Parnas and Fruman reportedly told the oligarch that they could introduce Vice President Mike Pence and Energy Secretary Rick Perry to Zelensky officials, in exchange for a fee. Kolomoisky has said that after the two men indicated they also wanted to arrange a meeting between Giuliani and Zelensky, he told them to get out.

“I say, ‘Did you see a sign on the door that says, ‘Meetings with Zelensky arranged here’?” Kolomoisky told The New York Times earlier this month. “They said, ‘No.’ I said, ‘Well then, you’ve ended up in the wrong place.’”

Giuliani sent an acrimonious tweet about Kolomoisky after his meeting with Parnas and Fruman.

Questions about Zelensky’s relationship with Kolomoisky percolated during his campaign and into his presidency. Zelensky grew prominent while starring in a TV show that aired on a channel Kolomoisky controls. And Kolomoisky returned to Ukraine from self-imposed exile in Israel and Switzerland after Zelensky’s election.

Despite the criticism from State Department officials and Giuliani, Bohdan remains Zelensky’s chief of staff.