A Republican former congressman turned lobbyist repeatedly pushed for the dismissal of U.S. ambassador to Ukraine Marie Yovanovitch, an action later taken by President Donald Trump after he was urged to do so by his personal lawyer Rudy Giuliani, a U.S. diplomat said in testimony on Wednesday.

Catherine Croft and Christopher Anderson, Ukraine specialists at the State Department, became the latest current and former U.S. officials called as witnesses in the Democratic-led impeachment inquiry against the Republican president in the House of Representatives, Reuters said.

Read alsoYovanovitch is latest casualty of Trump war on career diplomats – media

Croft, who testified for roughly five hours after being subpoenaed, said she was a member of the National Security Council (NSC) staff at the White House from July 2017 to July 2018.

"During my time at the NSC, I received multiple calls from lobbyist Robert Livingston, who told me that Ambassador Yovanovitch should be fired. He characterized Ambassador Yovanovitch as an 'Obama holdover' and associated with George Soros," Croft said in her opening statement to lawmakers, posted online by the Washington Post.

"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 Ambassador Yovanovitch," Croft said.

Soros is a wealthy financier often assailed by conservatives and known for his support of liberal causes. Barack Obama was Trump's Democratic predecessor.

The impeachment inquiry focuses on a July 25 telephone call in which Trump asked Ukrainian President Volodymr Zelensky to investigate Democratic political rival Joe Biden, a former U.S. vice president, and his son Hunter, who had served as a director for Ukrainian energy company Burisma. Trump has denied wrongdoing.

Trump abruptly removed Yovanovitch in May after allies of the president leveled unsubstantiated charges of disloyalty and other allegations against her.

Giuliani has said he went to Trump and the State Department as part of his effort to have her removed from the post at a time when he was seeking to persuade Ukraine to open an investigation of Biden, a contender for the Democratic nomination to face Trump in the November 2020 U.S. election.

The testimony revealed a previously unknown role for Livingston, who played a prominent role in the Republican-led drive to impeach Democratic President Bill Clinton in the 1990s, in the Ukraine controversy. Livingston was yet another well-connected Republican advocating against Yovanovitch, including Trump's son, Donald Trump Jr., Giuliani and former Republican congressman Pete Sessions.

Lobbying disclosure filings with the Justice Department show Livingston's firm represented two Ukrainian clients in Washington. They are former Ukrainian Prime Minister Yulia Tymoshenko, who mounted an unsuccessful run for president this year in the election won by Zelensky in a landslide in April, and an association of Ukrainian metal producers.

The filings revealed a connection between Livingston's firm and Giuliani, showing that Republican former congressman Bob McEwen of Ohio, working as a consultant to the Livingston Group, introduced Tymoshenko to Trump's lawyer last December.

The filings show that Livingston called Croft in May 2018, and contacted Anderson in November and December 2018.

Livingston, from Louisiana, was once one of the most powerful Republicans in Washington and had been in line to become House speaker. But he quit in 1998, saying he could not lead the effort to impeach Clinton for lying about a sexual relationship with an intern because he himself had engaged in an extramarital affair.

His firm did not immediately respond to a request for comment, Reuters said.

Croft said she told Fiona Hill, Trump's former top Russia adviser, and George Kent, a senior State Department Ukraine expert, about Livingston's efforts concerning Yovanovitch but was "not aware of any action that was taken in response."

Anderson, in his opening statement seen by Reuters, also mentioned Giuliani's actions. Before Zelensky's inauguration in May, Anderson said "my colleagues and I saw a tweet by Rudolph Giuliani" alleging that Ukraine’s incoming leader "was surrounded by enemies of President Trump." Anderson said he sought to counter that "negative narrative."