KYIV, Ukraine — A 2018 meeting between Rudy Giuliani and a Ukrainian politician that was brokered by the firm of a Republican lobbyist tarnished by scandal may be a key episode for investigators looking into Giuliani's backchannel diplomatic campaign in Ukraine, according to new claims by the country's former top prosecutor.

The Dec. 7 meeting between Giuliani and ex-Ukrainian prime minister Yulia Tymoshenko in Washington was set up by the lobbying firm of Bob Livingston, a former GOP congressman who State Department official Catherine Croft testified last week had called her multiple times in 2018 to urge the dismissal of U.S. ambassador to Ukraine Marie Yovanovitch.

Officially, the meeting concerned "the escalation of Russia's war against Ukraine and the U.S.'s assistance to our country, including weapons to counter Russian aggression," Tymoshenko's Fatherland party said at the time on its website.

But former Ukrainian Prosecutor General Yuriy Lutsenko, who U.S. prosecutors allege directed a plot to oust Yovanovitch, said in an interview with BuzzFeed News, the Organized Crime and Corruption Reporting Project (OCCRP) and NBC News that the meeting ended up producing another result — Giuliani extended an invitation to him to meet and discuss former Vice President Joe Biden's son, Hunter, and his work for Ukrainian gas company Burisma.

Lutsenko has made and retracted several claims since 2017 that were allegedly meant to curry favor with the Trump administration. But if substantiated, Lutsenko's assertion would add yet another name to the list of top Ukrainian officials who played a role in helping Giuliani's off-the-books investigation. That campaign saw him meet with current and former Ukrainian prosecutors who furnished him with unverified allegations involving the Bidens, Yovanovitch, and allegations of "Ukrainian interference" in the 2016 election.

A spokeswoman for Tymoshenko denied that she had discussed anything related to the Bidens with Giuliani in the meeting, or that he had asked her to put him in touch with Lutsenko.

Asked by a reporter at Ukraine's parliament if she had connected Giuliani and Lutsenko, Tymoshenko said, "That is categorically not true."

Giuliani didn't respond to requests for comment on his meeting with Tymoshenko.

Prosecutor General of Ukraine Yuriy Lutsenko speaks at a trial in Kyiv in 2017. Danil Shamkin / NurPhoto via Getty Images file

Lutsenko's claim also deepens questions about Livingston's involvement in the Trump camp's Ukraine push.

On Friday, a source with knowledge of the matter confirmed that federal prosecutors in New York who are investigating the actions of Giuliani associates Lev Parnas and Igor Fruman are also looking into whether Livingston was in touch with Giuliani about ousting Yovanovitch. The source said Livingston is not a target of the investigation.

Livingston told NBC News he didn't know about the meeting with Tymoshenko, who at the time was the frontrunner to become Ukraine's next president, until it was over. Asked what the meeting was about, Livingston said, "I wasn't there. I hear [Giuliani] hustled for business, but that was third hand."

Livingston, who was poised to become speaker of the house in 1998 amid impeachment proceedings against President Bill Clinton, instead announced his resignation from Congress after Hustler publisher Larry Flynt threatened to expose his extramarital affairs. He founded the Livingston Group in 1999 soon after leaving Congress.

Rep. Robert Livingston, R-LA, speaks to reporters on Dec. 17, 1998, two days before he announced he would be resigning from Congress. Paul J. Richard / AFP - Getty Images

Christine Croft told a House committee last week that she received phone calls from Livingston in the summer of 2018, pressing for the dismissal of Yovanovitch. "It was not clear to me at the time — or now — at whose direction or at whose expense Mr. Livingston was seeking the removal of Amb. Yovanovitch," she said.

Croft, a foreign service officer and former member of the National Security Council (NSC), began serving in May as deputy to Kurt Volker, the U.S. special envoy to Ukraine.

Livingston declined to comment about Croft.

Amb. Yovanovitch was recalled from Ukraine in May after a chorus of criticism from conservative figures that echoed grievances put forward by Ukrainian officials who had run afoul of the embassy's anti-corruption agenda.

An investigation by BuzzFeed News and OCCRP in July found that Giuliani associates Parnas and Fruman lobbied at least one congressman, former Rep. Pete Sessions, in May last year to dismiss Yovanovitch. Sessions, who later received campaign donations from both men, wrote a private letter to Secretary of State Mike Pompeo that month urging the ambassador's ouster. Sessions has now returned the money.

The Livingston Group and Tymoshenko

Filings with the Justice Department show that starting in April 2018, the Livingston Group began work for two entities with links to Ukraine, but not directly for Tymoshenko. One client, a Ukrainian metals industry association called UKRMETALURGROM paid the firm $20,000 month between April and July.

Livingston called and emailed Croft as part of the UKRMETALURGROM contract on May 17, 2018, to discuss U.S. steel tariffs and the forthcoming visit by a Ukrainian economic official, Justice Department filings show.

Oleksandr Kalenkov, president of UKRMETALURGROM, said the Livingston Group was hired purely to lobby on steel tariffs and the work had nothing to do with Tymoshenko.

Rep. Robert Livingston, D- La., House Appropriations Committee Chairman in July 1995. Laura Patterson / CQ-Roll Call

"I have not personally contacted Amb. Yovanovitch on this issue and there were no conversations, no contacts regarding Yovanovitch through me, between Livingston and I, absolutely not," Kalenkov said.

The December meeting with Giuliani was organized as part of Livingston Group's lobbying for ITBC LLC, a Maryland-registered company set up just six weeks earlier. While officially working for the Maryland company, the Livingston Group's filings show that until July this year it represented interests related to Tymoshenko in the United States.

Regarding his company's contracts with ITBC LLC and UKRMETALURGROM, Livingston said, "There's no relation between the two."

The Livingston Group's contract with ITBC LCC is to represent "a group of persons supporting reform in Ukraine," the lobbyist reported to the U.S. Justice Department's division that oversees foreign lobbying. "They believe Mrs. Tymoshenko is best suited to lead Ukraine in its ongoing battle with Russian military and economic aggression."

Its contract with Tymoshenko lasted almost a year and was worth $180,000.

Contacted by phone, Sergei Krasnitski, the Ukrainian-American registered agent of ITBC LLC, declined to say who owned the company.

"I wasn't aware that there was a meeting [between Giuliani and Tymoshenko," he said. "If the Livingston group filed that there was a meeting then it must be true."

The meeting with Giuliani was just one event organized under the ITBC LLC contract by the Livingston Group for Tymoshenko's visit to the U.S., according to lobbying filings. She also met with Volker, the former U.S. special envoy for Ukraine; George Kent, the deputy assistant Secretary of State for European and Eurasian affairs; and Rep. Adam Schiff of California, the Democratic chairman of one of the committees conducting the impeachment inquiry.

On Dec. 5, Tymoshenko was scheduled to meet Giuliani and Ed Meese, who served as attorney general in the Reagan administration. But the scheduled meeting didn't happen, according to Bob McEwan, a lobbyist contracted by the Livingston Group who set up the meeting, because Tymoshenko didn't show up.

He said the meeting was rescheduled and Tymoshenko met with Giuliani later in her visit, and that Meese was not present for that session. Her Fatherland party dated the makeup session with Giuliani two days later, on Dec. 7.

Also present at the meeting were two other high-ranking Fatherland party politicians, Deputy Chairman Hryhoriy Nemyria, and a Parliament committee chairman, Serhiy Vlasenko. Calls to both of them were referred to the party spokeswoman, who declined to comment.

The work done by Livingston is just one of several U.S. lobbying contracts in recent years linked to Tymoshenko that have been carried out with the involvement of little-known companies, some based offshore.

ITBC LLC, the company behind one of the Livingston contracts, in August last year also hired Naomi Decter Munson, a Washington, D.C.-based media consultant for $15,000 a month.

Contacted by reporters, Decter Munson said she only worked for "a few weeks for some businessmen who were supporting Yulia Tymoshenko" but she fired them after they rejected her ideas for how to get media coverage.

Until early this year, Tymoshenko was also being indirectly represented by another lobbyist, Wiley Rein. Wiley Rein stated in Justice Department filings that it worked for Tymoshenko's husband Oleksandr, as well as a British company called Aveiro LP, which was in turn owned by two companies in Belize, a small Central American country known as a haven for corporate secrecy.

Kurt Volker, a former special envoy to Ukraine, leaves after a closed-door interview with House investigators at the Capitol on Oct. 3, 2019. Jose Luis Magana / AP

Justice Department filings show that Wiley Rein also organized meetings for Tymoshenko during her December visit to the U.S. with congressmen, diplomats and journalists. The lobbying firm disclosed in March this year that Tymoshenko was the beneficiary of this work.

The filings also show the company received close to $130,000 last year from half a dozen companies based in locations including Florida, the United Kingdom and Belize for legal and consulting fees related to the contract.

Wiley Rein did not respond to requests for comment.

Tymoshenko and Lutsenko

Yulia Tymoshenko served as Ukraine's prime minister from January to September 2005 and again from December 2007 to 2010. She was in the midst of her third unsuccessful campaign for president when she met with Giuliani in 2018.

While she was initially the frontrunner, Tymoshenko came in third in the initial round of voting. In an April run-off, political neophyte Volodymyr Zelenskiy defeated the second-place finisher, incumbent President Petro Poroshenko, to win the presidency in a landslide. Zelenskiy's July phone call with President Donald Trump, in which Trump pressed Zelenskiy to agree to investigate the Bidens, sparked the current House impeachment inquiry.

Lutsenko served as interior minister between February 2005 and December 2006. Part of his stint was during Tymoshenko's first term as prime minister. The two would later have a falling out.

In 2011, Tymoshenko was convicted of abuse of office charges for brokering a deal between the state energy company, Naftogaz, and Russia in 2009. The charges were widely seen in the West as politically motivated and she had her conviction overturned after 2014 protests ousted Ukrainian President Viktor Yanukovych.

Lutsenko was sentenced in February 2012 to four years imprisonment for embezzlement and abuse of office — charges that were also widely viewed as politically motivated. He was released in 2013 after being pardoned by Yanukovych.