WASHINGTON (AP) — A State Department Foreign Service officer is telling House impeachment investigators that former national security adviser John Bolton cautioned him that Rudy Giuliani "was a key voice with the president on Ukraine" and could complicate U.S. goals in the Eastern European country.

The testimony on Wednesday from Christopher Anderson makes clear that administration officials were concerned about Giuliani's back-channel involvement in Ukraine policy and his push for investigations even before the July phone call between President Donald Trump and his Ukraine counterpart that's now at the center of the House impeachment inquiry. On that call, Trump prodded Ukraine President Volodymyr Zelenskiy to investigate Democratic rival Joe Biden.

Anderson describes a June meeting in which he said Bolton expressed support for the administration's goals of strengthening energy cooperation between the U.S. and Ukraine and getting Zelenskiy to undertake anti-corruption reforms.

"However, he cautioned that Mr. Giuliani was a key voice with the president on Ukraine which could be an obstacle to increased White House engagement," Anderson will say, according to a copy of his prepared remarks obtained by The Associated Press. Giuliani is Trump's personal lawyer.

Anderson, scheduled to appear in private late Wednesday, is a career Foreign Service officer who was special adviser for Ukraine negotiations until this past June.

In his opening statement, he traces his unease with developments and statements in the U.S. that he felt threatened to set back relations between the U.S. and Ukraine. That includes a tweet from Giuliani that Anderson said alleged that Zelenskiy "was surrounded by enemies of President Trump" and the abrupt recall earlier this year of Marie Yovanovitch, then U.S. ambassador to Ukraine.

In addition, senior White House officials blocked an effort by the State Department to release a November 2018 statement condemning Russia's attack on Ukrainian military vessels.

"To counter the negative narrative," Anderson says he pushed for a high-level delegation of U.S. officials to attend Zelenskiy's inauguration. Several senior officials ultimately did go.

Another Foreign Service officer testifying Wednesday, Catherine Croft, says that during her time at the National Security Council, she received multiple phone calls from lobbyist Robert Livingston telling her Yovanovitch should be fired.

"He characterized Ambassador Yovanovitch as an 'Obama holdover' and associated with George Soros. 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," she will say.

Both witnesses were instructed by the administration to not testify but appeared in response to subpoenas from the House, according to a statement from their attorney Mark MacDougall. The lawyer cautioned lawmakers that neither of his clients is the whistleblower whose complaint triggered the impeachment inquiry and that he would object to any questions aimed at identifying that person.

Their testimony follows that of Alexander Vindman, an Army officer with the National Security Council who testified that he twice raised concerns over the administration's push to have Ukraine investigate Democrats and Joe Biden.

Vindman, a lieutenant colonel who served in Iraq and later as a diplomat, was the first official to testify who actually heard Trump's July 25 call with Zelenskiy. He reported his concerns to the NSC's lead counsel.

Vindman also told investigators Tuesday that he tried to change the White House's rough transcript of the call by filling in at least one of the omitted words, "Burisma," a reference to the company linked to Biden and his son, according to people familiar with his testimony. But Vindman was unsuccessful.

He also testified that some of the ellipses omitted Trump saying there are recordings of Joe Biden discussing corruption in Ukraine, according to people familiar with Tuesday's closed-door testimony.

Vindman's concerns, though, were far bigger than the transcript. And lawmakers said his failed effort to edit it didn't significantly change their understanding of what transpired during Trump's call that sparked the impeachment inquiry.

Vindman's arrival in military blue, with medals, created a striking image at the Capitol as the impeachment inquiry reached deeper into the White House. He testified for more than 10 hours.

"I was concerned by the call," Vindman said, according to prepared remarks . "I did not think it was proper to demand that a foreign government investigate a U.S. citizen, and I was worried about the implications for the U.S. government's support of Ukraine."

Vindman, a 20-year military officer, added to the mounting evidence from other witnesses — diplomats, defense and former administration officials — who are corroborating the initial whistleblower's complaint against Trump and providing new details ahead of a House vote in the impeachment inquiry.

The inquiry is looking into Trump's call, in which he asked Zelenskiy for a "favor" — to investigate Democrats — that the Democrats say was a quid pro quo for military aid and could be an impeachable offense.

Vindman's testimony came the day after Speaker Nancy Pelosi announced the House would vote on a resolution to set rules for public hearings and a possible vote on articles of impeachment.

Thursday's vote would be the first on the impeachment inquiry and aims to nullify complaints from Trump and his allies that the process is illegitimate and unfair.

White House press secretary Stephanie Grisham said the resolution merely "confirms that House Democrats' impeachment has been an illegitimate sham from the start as it lacked any proper authorization by a House vote."

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Associated Press writers Zeke Miller, Padmananda Rama, Matthew Daly, Laurie Kellman, Eric Tucker and Alan Fram contributed to this report.