"Wacky Omarosa, who got fired 3 times on 'the Apprentice, ' now got fired for the last time", Trump tweeted.
On Monday, Manigault-Newman released a new recording that appeared to reveal that Trump was unaware she was being dismissed from the White House.
Trump criticized her job performance at the White House.
On Monday, he took the criticism a step further, calling his former aide "vicious" and "not smart". "People in the White House hated her".
"No... I, I, Nobody even told me about it", Trump replies.
When she asks whether the president was aware of her pending termination, Kelly, on the audio recording, purportedly tells her that "this is a non-negotiable discussion" and that her firing was related to "pretty serious integrity violations".
Manigault Newman, who is African-American, also writes in her incendiary memoir Unhinged - set to hit bookshelves Tuesday - that Trump uttered a racial slur "multiple times" during the making of his hit show The Apprentice prior to his presidential run, and that there are tapes to prove it.
Omarosa Manigault Newman also claimed that Americans were being kept in the dark about their president's mental decline, saying: "I was complicit with the White House deceiving this nation".
Manigault Newman, who was dramatically fired from the West Wing previous year by chief of staff John Kelly, claims she has a recording of the conversation of Kelly attempting to fire her, as well a recordings of conversations with the president.
After "Today" aired the new audio on Monday, Manigault Newman was asked if the President was lying about whether he knew about her termination. Traditionally chiefs of staff do handle hiring and firing in the White House. She says she has other tapes she secretly made at the White House.
According to the New York Times, she had annoyed colleagues at the White House - but not Mr Trump himself - through her "damn-the-rules" behaviour.
Manigault-Newman described that comment as a "very obvious...threat" on NBC's "Meet the Press" on Sunday. "I never expected him to lie to the country..."
Parts of her conversation with Kelly were played on the air.
"You know, in 2003 Donald Trump was sharp". I don't love you leaving at all.
"No ... I, I, nobody even told me about it", the president appears to respond. "Of course, Savannah, she handled it beautifully, but Omarosa is approaching a lot of these interviews like she's being attacked with every question, and she's not". During her brief tenure at the White House, she served, per Reuters, as assistant to the president and as director of communications for the Office of Public Liaison. "She never made it, never will", Trump tweeted on Monday, admitting that his response to her claims were "not presidential".
"I have heard the tape", she said, adding that three sources she talked to for her book relayed the same story.
He continued: 'Then on top of that, her character and her integrity have been impugned beyond measure.