President Trump Donald John TrumpBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Pelosi: Trump Supreme Court pick 'threatens' Affordable Care Act MORE's personal lawyer Rudy Giuliani Rudy GiulianiThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting CIA found Putin 'probably directing' campaign against Biden: report Democrats fear Russia interference could spoil bid to retake Senate MORE met this week with a former Ukrainian prosecutor who made claims about former Vice President Joe Biden Joe BidenBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Joe Biden should enact critical government reforms if he wins MORE and the 2016 election that are now central to the House's impeachment inquiry, The New York Times reported Wednesday.

The Times, citing people familiar with the meeting, reported that Giuliani met in Budapest on Tuesday with former Ukrainian prosecutor Yuriy Lutsenko, who has made claims about an energy company where Biden's son Hunter Biden sat on the board.

Giuliani also reportedly met Wednesday in Kyiv with other former Ukrainian prosecutors including Viktor Shokin and Kostiantyn H. Kulyk.

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The former prosecutors have played a role in pushing damaging claims about Biden, a former U.S. ambassador to Ukraine and Ukrainians who spread unflattering information about former Trump campaign chairman Paul Manafort Paul John ManafortFBI official who worked with Mueller raised doubts about Russia investigation Our Constitution is under attack by Attorney General William Barr Bannon trial date set in alleged border wall scam MORE, according to The Times.

The newspaper reported that Giuliani is using the trip to prepare episodes of a documentary series for conservative TV outlet One America News.

Giuliani said in a Tuesday tweet that he was "working on an important project" with OAN that is meant to bring people information that has been "covered up" in the House's impeachment proceedings into Trump.

On Thursday, Giuliani met with independent Ukraine lawmaker Andriy Derkach, who posted a picture with the former New York mayor on Facebook, The Washington Post reported.

“Rudolph Giuliani has arrived in Kyiv,” Derkach said in his post. “We met up immediately to discuss the establishment of the Friends of Ukraine STOP Corruption interparliamentary group.”

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Formerly a member of a pro-Russian party in Ukraine’s parliament, Derkach reportedly said that he wrote letters earlier in the week to Sen. Lindsey Graham Lindsey Olin GrahamHarris slams Trump's Supreme Court pick as an attempt to 'destroy the Affordable Care Act' Sunday shows preview: Lawmakers prepare for SCOTUS confirmation hearings before election Confirmation hearing for Trump's Supreme Court pick to start Oct. 12 MORE (R-S.C.), Rep. Devin Nunes Devin Gerald NunesOvernight Defense: Stopgap spending measure awaits Senate vote | Trump nominates former Nunes aide for intelligence community watchdog | Trump extends ban on racial discrimination training to contractors, military Trump nominates former Nunes aide to serve as intel community inspector general Sunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election MORE (R-Calif.) and White House acting chief of staff Mick Mulvaney Mick MulvaneyOn The Money: House panel pulls Powell into partisan battles | New York considers hiking taxes on the rich | Treasury: Trump's payroll tax deferral won't hurt Social Security Blockchain trade group names Mick Mulvaney to board Mick Mulvaney to start hedge fund MORE, asking for their participation.

Derkach told the Post that he believes that their involvement would help expose the misuse of U.S. aid by Ukrainian officials.

“We sent our proposal. We’re waiting for a reaction, an answer,” Derkach said.

“We’re waiting to see how much this is something that the congressmen and senators are in need of. If they want to work together, we’re ready,” he added.

Derkach also said that he gave Giuliani documents regarding allegations relating to the inefficient use of U.S. money on projects in Ukraine, but that the documents didn’t mention the Bidens.

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However, according to the Post, Derkach previously led calls to investigate the Bidens and supposed Ukrainian interference in the 2016 election, theories that have been thoroughly debunked by analysts.

Trump's and Giuliani's dealings with Ukraine have come under scrutiny as part of the House's impeachment hearing. On Wednesday, constitutional scholars testified before the House Judiciary Committee as part of the impeachment probe.

Trump and Giuliani have denied wrongdoing.

This story was updated at 11:59 on Dec. 6.

Marty Johnson contributed.