Alexander Vindman / REUTERS

U.S. President Donald Trump has explained why he fired Lt. Col. Alexander Vindman, a National Security Council (NSC) expert on Ukraine.

Trump says he does not know Vindman, Ukraine's European Pravda news outlet reported.

"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…" the U.S. President said on Twitter on February 8.

Read alsoNYT: Trump fires impeachment witnesses Gordon Sondland, Alexander Vindman in post-acquittal purge

"[Vindman] 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,'" he said.

As was reported, Trump on February 7 fired two key impeachment witnesses, dismissing Vindman, the top Ukraine expert at the council, and U.S. Ambassador to the European Union Gordon Sondland.