U.S. President Donald Trump fired two key impeachment witnesses on Friday, dismissing Army Lieutenant Colonel Alexander Vindman, White House's top Ukraine expert, and Gordon Sondland, U.S. Ambassador to the European Union.

U.S. Ambassador to the European Union Gordon Sondland is sworn in to testify before the House Intelligence Committee on Capitol Hill in Washington, November 20, 2019. (Photos: AP)

Vindman was escorted out of the White House where he had worked on the National Security Council (NSC), his lawyer David Pressman said in a statement, adding that the move was retribution for Vindman's testimony.

"There is no question in the mind of any American why this man's job is over, why this country now has one less soldier serving it at the White House. LTC Vindman was asked to leave for telling the truth," Pressman said.

While Sondland announced in a statement later on Friday that he is being recalled from his post.

"I was advised today that the President intends to recall me effective immediately as United States Ambassador to the European Union," Sondland said in the statement

"I am grateful to President Trump for having given me the opportunity to serve, to Secretary Pompeo for his consistent support, and to the exceptional and dedicated professionals at the U.S. Mission to the European Union. I am proud of our accomplishments. Our work here has been the highlight of my career."

'I will be fine telling the truth'

Vindman testified to the House of Representatives impeachment inquiry in November that Trump made an improper demand of Ukrainian President Volodymyr Zelenskiy in a July phone call that became the centerpiece of the probe of the Republican president.

Lt. Col. Alexander Vindman is sworn in to testify before the House Intelligence Committee on Capitol Hill during a public impeachment hearing of U.S. President Donald Trump in Washington, November 19, 2019. 

Vindman told a Democratic-run committee: "I couldn't believe what I was hearing" in the phone call. Trump asked Zelenskiy to launch investigations into both Democratic rival Joe Biden and a widely debunked conspiracy theory that Ukraine, not Russia, was behind meddling in the 2016 U.S. presidential election.

During that appearance, Vindman downplayed concerns that he would suffer payback for speaking out. "I will be fine telling the truth," he said.

Vindman's two-year stint at the White House was due to end in July.

Trump emerged victorious from his trial this week with a vote in the Senate, controlled by fellow Republicans who rejected abuse of power and obstruction of justice charges.

Asked earlier on Friday about media reports that he might remove Vindman, Trump told reporters: "I'm not happy with him. You think I'm supposed to be happy with him? They're going to be making that decision."

Michael Volkov, who represented Alexander Vindman when he testified in the impeachment inquiry, said Vindman's twin brother, Yevgeny Vindman, was escorted off the White House grounds at the same time.

Lt. Col. Alexander Vindman (L), walks with his twin brother, Lt. Col. Yevgeny Vindman (R), after testifying before the House Intelligence Committee on Capitol Hill in Washington, November 19, 2019.

Yevgeny Vindman, also an Army lieutenant colonel, worked for the NSC as a lawyer.

An Army spokesperson said both brothers had been reassigned to the Army, but declined to provide further information "out of respect for their privacy."

A lawyer for Yevgeny Vindman did not immediately respond to a request for comment.

A spokesperson for the security council declined to comment.

Representative Eliot Engel, Democratic chairman of the House Foreign Affairs Committee, said the decision to remove Alexander Vindman was "shameful."

"This president believes the only loyalty that matters is loyalty to him personally," Engel said in a written statement.