An attorney for Lev Parnas, an associate of Rudy Giuliani, is claiming his client traveled to Kiev shortly before the inauguration of Ukrainian President Volodymyr Zelensky this year to demand the new administration publicly announce an investigation into 2020 presidential candidate Joe Biden and his son.

Parnas' lawyer confirmed to Fox News that his client told Ukrainian officials that Vice President Mike Pence would not attend the swearing-in of the new president and the United States would freeze aid to the Eastern European nation if the demands were not met.

The claim by Parnas, who has been preparing to testify in the House Intelligence Committee’s impeachment inquiry into President Trump, directly challenged the accounts by Trump and Ukrainian officials that have been at the heart of the congressional probe. Parnas’ claim also directly tied Giuliani, Trump’s personal attorney, to threats of retribution if Ukrainian officials did not comply with the demands – something Giuliani steadfastly has denied.

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Parnas’ story, however, has been contradicted by a number of people, including his business partner Igor Fruman, who also was present at a meeting with the Ukrainians and claimed neither the issue of foreign aid nor the vice president’s attendance at the inauguration was raised.

Both Parnas and Fruman pleaded not guilty two weeks ago to campaign-finance charges connected to political donations to a pro-Trump super PAC. They were accused of using a limited liability company, Global Energy Producers (GEP), to make donations in American elections to advance the political interests of at least one Ukrainian government official.

Giuliani had hired Parnas and Furman to try persuading Ukrainian officials to investigate Biden and his son Hunter for possible corruption. That relationship has now become another arm of the growing impeachment inquiry against Trump, as three House committees have been looking into whether Trump tried to persuade Zelensky to investigate the Bidens by withholding U.S. military aid during a July 25 phone call between the two leaders.

The first public hearings in the impeachment inquiry are scheduled to be held this Wednesday and Friday, featuring current and former officials with knowledge of the Ukraine controversy.

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The first public hearing is to feature Bill Taylor, the acting U.S. ambassador to Ukraine, who already testified behind closed doors to congressional investigators that the president pushed Ukraine to investigate election interference, Biden and his son and their Ukraine dealings.

George Kent, the deputy assistant Secretary of State, is also scheduled to appear with Taylor. Kent testified behind closed doors last month; he told the committees he had concerns about Hunter Biden’s role on the board of Ukrainian natural-gas firm Burisma Holdings in 2015 but was rebuffed by the former vice president’s staff, which said the office was preoccupied with Beau Biden’s cancer battle.