Donald Trump has appeared to admit he fired a senior White House official in part for the aide’s involvement in the impeachment inquiry.

Lt Col Alexander Vindman, a Russia and Ukraine expert on the National Security Council (NSC), was escorted from the White House on Friday after the US president ordered his removal.

He had given evidence to House committee hearings which led to Mr Trump being impeached on charges of abuse of power and obstructing Congress relating to a campaign by the president to pressure Ukraine into investigating Joe Biden, a political rival.

“Fake News @CNN & MSDNC keep talking about ‘Lt. Col.’ Vindman as though I should think only how wonderful he was,” the US president tweeted on Saturday morning.

“Actually, I don’t know him, never spoke to him, or met him (I don’t believe!) but, he was very insubordinate, reported contents of my ‘perfect’ calls incorrectly, & was given a horrendous report by his superior, the man he reported to, who publicly stated that Vindman had problems with judgement, adhering to the chain of command and leaking information. In other words, ‘OUT’.”

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Mr Trump’s son, Donald Trump Jr, had earlier appeared to suggest Lt Col Vindman and Gordon Sondland, who was recalled as US ambassador to the European Union, were sacked for their testimony in the inquiry.

Mr Trump was acquitted this week by Republican allies in the Senate, even though some admitted they did not dispute the allegations against him.

Amid speculation that Lt Col Vindman was likely to be fired, the president on Friday said he was unhappy with him but appeared to suggest the decision would be made by someone else, saying: “Well, I’m not happy with him. You think I’m supposed to be happy with him? I’m not. They’ll make that decision.”

He did not specify who “they” referred to but his comments came against a background of suggestions that the NSC, which is thought to have about 180 staff, could be reduced in size.

Lt Col Vindman’s twin brother, Yevgeny Vindman, was also fired from his position as a lawyer with the NSC, although he had no involvement in the impeachment process.

Both are expected to return to the Department of Defence.

Lt Col Vindman’s attorney, David Pressman, said in a statement: “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.

“Lt Col Vindman was asked to leave for telling the truth. His honour, his commitment to right, frightened the powerful.”

The decorated Iraq veteran had listened in to a 25 July call between Mr Trump and Volodymyr Zelensky in which the US president pressed his Ukrainian counterpart to launch investigations into his Democratic political rivals.

Lt Col Vindman testified that he was unsettled by the call. In an emotional statement at the end of his testimony he thanked his late father for bringing him and his family to America from the former Soviet Union, saying: “Do not worry. I will be fine for telling the truth.” At another point, he said: “Here, right matters.”

Trump calls Russia probe 'bullshit'

Mr Sondland had been involved in efforts in Ukraine to press officials to investigate Mr Trump’s political opponents. He told the impeachment hearings there had been a “quid pro quo”, involving the withholding of US military aid until Ukraine announced the investigations the presidents wanted.

He also claimed other top figures were “in the loop”, including vice-president Mike Pence, secretary of state Mike Pompeo and chief of staff Mick Mulvaney

Some of the other witnesses who gave evidence have already left their jobs, including former US ambassador to Ukraine Marie Yovanovitch, who was recalled in May after apparently getting in the way of efforts to pressure officials in Kiev to investigate Mr Trump’s rivals. In the 25 July phone call he appeared to threaten her, saying: “Well, she’s going to go through some things.”

Ms Yovanovitch retired last month. Her replacement, William Taylor, vice-presidential aide Jennifer Williams and NSC official Tim Morrison – all of whom also gave evidence – have also left their posts.

There is speculation that there may be more firings in the wake of Mr Trump’s Senate acquittal.

One name in the frame is Mr Mulvaney who did not testify, despite demands from the House of Representatives that he do so. However, he did admit at a White House press briefing that Mr Trump had withheld US military aid to Ukraine at least in part to pressure Kiev to investigate conspiracy theories about the Democratic Party, saying: “I have news for everybody: Get over it. There’s going to be political influence in foreign policy.”

Despite Mr Trump’s assertion that his job is safe for the time being, there are suggestions he will be replaced by Mark Meadows, a Trump loyalist currently serving as a Republican congressman for North Carolina.

The Washington Post reports that the president has discussed firing Michael Atkinson, the intelligence community’s inspector general, who passed on a complaint from a whistleblower about the 25 July phone call to Congress.