The unnamed Ukrainian official referenced in a federal indictment as directing a plot to oust the then-U.S. ambassador is Ukraine's former chief prosecutor Yuriy Lutsenko, according to a U.S. official familiar with the events.

According to the source, Lutsenko is the Ukrainian official who prosecutors say urged two associates of Rudy Giuliani to push for the removal of Marie Yovanovitch, the former U.S. ambassador to Ukraine who was forced out in May.

The associates, Lev Parnas and Igor Fruman, were arrested Wednesday night as they prepared to board a one-way flight out of the country at Dulles Airport near Washington, D.C.

"They sought political influence not only to advance their own financial interests, but to advance the political interests of at least one foreign official ⁠— a Ukrainian government official who sought the dismissal of the U.S. ambassador to Ukraine," Geoffrey Berman, U.S. attorney for the Southern District of New York, said at a Thursday news conference.

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The indictment says the efforts by Parnas and Fruman to remove then-Ambassador Marie Yovanovitch, a respected diplomat with deep knowledge of Ukraine, were "conducted, at least in part, at the request of one or more Ukrainian government officials."

Federal prosecutors didn't detail in the indictment or at a press conference why the unnamed Ukrainian official or officials allegedly urged Parnas and Fruman to scheme to push out Yovanovitch.

But two former U.S. officials said Lutsenko had sharp disagreements with Yovanovitch over his handling of corruption cases, and was also seeking to curry favor with the Trump administration.

Yovanovitch's ouster is now at the center of an impeachment inquiry by House Democrats, who accuse President Donald Trump of abusing his power by pressuring Ukraine to launch an investigation of Joe Biden, his political rival, and Biden's son.

Yovanovitch told Congress on Friday that President Trump wanted her removed as ambassador because of "unfounded and false claims by people with clearly questionable motives."

During the July 25 phone call with Ukrainian President Volodymyr Zelenskiy that is now at the center of the House impeachment inquiry, Trump referred to Yovanovitch as "bad news."

'Personal payback'

Lutsenko was the country's chief prosecutor under the previous Ukrainian government, serving from May 2016 to August 2019.

When approached by Giuliani and his associates, Parnas and Fruman, Lutsenko was facing an uncertain political future. The Giuliani team saw U.S. Ambassador Yovanovitch as an obstacle to their objectives — digging up derogatory information on former vice president Biden and smoothing the way for a possible natural gas deal in Ukraine, former officials said.

"[Lutsenko's] incentive to help was to take out the ambassador," said a former senior diplomat with experience in the region. "He was angry at criticism from the U.S. embassy over the slow pace of reform in the justice sector."

"There was this personal payback dimension."

Lutsenko could not be reached for comment.

Lutsenko's name had surfaced in the impeachment inquiry against President Trump even before the indictment against Fruman and Parnas was unsealed. In his July call with Ukrainian President Zelenskiy, Trump praised an unnamed prosecutor and lamented that he was "shut down," an apparent reference to Lutsenko.

"I heard you had a prosecutor who was very good and he was shut down and that's really unfair," Trump said in the call. "A lot of people are talking about that."

Lutsenko told NBC News last month that he's known Giuliani for "many years" and met with him while vacationing in New York.

Lutsenko said he counted Giuliani as a friend and has spoken to him "maybe 10 times."

Lutsenko said they discussed former Vice President Biden and his son, Hunter, and talked "about our system, about some of our law enforcement divisions and possibilities to cooperate."

In the indictment unsealed Thursday, federal prosecutors accused Parnas and Fruman of funneling foreign money to U.S. politicians in violation of federal campaign finance laws.

The indictment said Parnas and Fruman enlisted the help of a congressman in their effort to force out Yovanovitch.

Multiple senior U.S. law enforcement officials told NBC News that the "Congressman-1" referenced in the indictment is former Rep. Pete Sessions, R-Texas. The two men committed to raising $20,000 for the then-lawmaker, the indictment alleged.

Sessions said Friday that he would return any campaign donations from Parnas and Fruman.

Dan De Luce reported from Washington.