Marie Yovanovitch, the ousted U.S. ambassador to Ukraine, told House impeachment investigators Friday that President Donald Trump had personally pressured the State Department to remove her, even though a top department official assured her that she had "done nothing wrong."

Yovanovitch said that after she was abruptly recalled from her post in the spring, Deputy Secretary of State John Sullivan told her that the president had lost confidence in her, according to her prepared remarks.

"He added that there had been a concerted campaign against me, and that the department had been under pressure from the president to remove me since the summer of 2018," Yovanovitch said.

"He also said that I had done nothing wrong and that this was not like other situations where he had recalled ambassadors for cause," she added.

Yovanovitch, a career diplomat who said she was informed of her ouster in April, said in her statement that she was "incredulous that the U.S. government chose to remove an ambassador based, as best as I can tell, on unfounded and false claims by people with clearly questionable motives."

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She warned that allowing misinformation to subvert U.S. diplomats like herself would "harm" the U.S.

"The harm will come when private interests circumvent professional diplomats for their own gain, not the public good," she said. "The harm will come when bad actors in countries beyond Ukraine see how easy it is to use fiction and innuendo to manipulate our system."

Yovanovitch appeared for her expected closed-door deposition before the House Intelligence, Oversight and Foreign Affairs Committees as part of their investigations into Trump’s efforts to persuade Ukraine's new government to commit publicly to investigate corruption and the president's political opponents.

It had been unclear right up until Yovanovitch arrived whether she would appear because she still works for the State Department. The White House had vowed that administration officials would not cooperate with the impeachment probe.

Hours into her testimony, the chairmen of the three committees released a statement saying that the State Department, at the behest of the White House, had directed her not to appear for her voluntary interview. In response, the House Intelligence Committee issued a subpoena to compel her Thursday night.

"This duly authorized subpoena is mandatory, and the illegitimate order from the Trump Administration not to cooperate has no force. As is required of her, the Ambassador is now complying with the subpoena and answering questions from both Democratic and Republican members and staff," Rep. Adam Schiff, the chairman of the Permanent Select Committee on Intelligence, Rep. Elijah Cummings, the chairman of the Committee on Oversight and Reform and Rep. Eliot Engel, the chairman of the Committee on Foreign Affairs, said.

"Any efforts by Trump Administration officials to prevent witness cooperation with the Committees will be deemed obstruction of a co-equal branch of government and an adverse inference may be drawn against the President on the underlying allegations of corruption and coverup," the chairs added.

Rep. Eleanor Holmes Norton, D.C.'s nonvoting House delegate and a member of the Oversight Committee, said Yovanovitch was "acting like a true ambassador."

"She herself has been deeply involved and has been the object of false statements, and she's clearing that up," Holmes Norton said.

Holmes Norton added that "both sides are finding her very credible," and Yovanovitch had not indicted that anyone attempted to prevent her from answering questions from lawmakers as expected Friday.

Asked about whether Yovanovitch had spoken about Trump's personal lawyer, Rudy Giuliani, Holmes Norton said, "That is becoming very, very deep."

Yovanovitch had previously been scheduled to be deposed by the committees on Oct. 2, but the appearance was postponed.

In a letter to House Democrats last week, Secretary of State Mike Pompeo pushed back against Democrats' request to interview five current and former State Department employees, including Yovanovitch.

Yovanovitch has emerged as a potentially key figure in the investigation by House Democrats.