An attrney for the US official, a former White House expert on Ukraine, Lt. Col. Alexander Vindman, accused the US president of lying, BBC News reported.

David Pressman said the remarks were "obviously false" and that Mr Trump was in a "campaign of intimidation".

"While the most powerful man in the world continues his campaign of intimidation, while too many entrusted with political office continue to remain silent, Lieutenant Colonel Vindman continues his service to our country as a decorated, active duty member of our military."

Earlier, US President Donald Trump tweeted on his position in connection with Vindman's dismissal.

According to him, Vindman did not respect subordination.

"Fake News @CNN & MSDNC keep talking about “Lt. Col.” Vindman as though I should think only how wonderful he was. 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, &..." he tweeted.

Vindman was one of the dignitaries who testified under the impeachment procedure.