Rep. Eliot Engel pushed back Wednesday on President Donald Trump's claim that John Bolton didn't complain about his conduct toward Ukraine, revealing that Bolton, only days after being ousted as Trump's national security adviser, told him in a phone call to examine the ouster of the U.S. ambassador to Ukraine.

"President Trump is wrong that John Bolton didn't say anything about the Trump-Ukraine scandal at the time the President fired him," Engel, D-N.Y., chairman of the Foreign Affairs Committee, said in a statement. "He said something to me."

Engel said that he reached out to Bolton on Sept. 19 to ask if he would speak before the Foreign Affairs Committee regarding U.S. foreign policy. (Trump fired Bolton on Sept. 10; Bolton says he quit.) Engel said he then spoke with Bolton days later, in a call on Sept. 23, when Bolton "suggested to me — unprompted — that the committee look into the recall of Ambassador Marie Yovanovitch."

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That call took place the day before House Speaker Nancy Pelosi announced the House would begin its impeachment inquiry.

"He strongly implied that something improper had occurred around her removal as our top diplomat in Kyiv," Engel continued. "At the time, I said nothing publicly about what was a private conversation, but because this detail was relevant to the Foreign Affairs, Intelligence and Oversight Committees' investigation into this matter, I informed my investigative colleagues. It was one of the reasons we wished to hear from Ambassador Bolton, under oath, in a formal setting."

Engel's remarks come as Trump berated Bolton after he reportedly contradicted a key element of the president's impeachment defense in an upcoming book.

Earlier Wednesday, Trump asked: "Why didn't John Bolton complain about this 'nonsense' a long time ago, when he was very publicly terminated."

This week, The New York Times reported that, according to a manuscript of Bolton's book, Trump told Bolton in August that nearly $400 million in aid to Ukraine would not be released until the country provided all of the information it had in connection with the investigations into Democrats the president had sought. The manuscript has not been seen by NBC News.

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That reported conversation contradicts the president's impeachment defense, as Trump and allies have said the hold on military aid and investigations were not linked. Trump said he "NEVER" had such a conversation with Bolton.

In a statement Wednesday, Sen. Lindsey Graham, R-S.C., seemed to suggest that Trump should stop publicly blasting Bolton because it could increase the chance of him being called to testify before the Senate, saying he is "concerned when John Bolton’s credibility is attacked, it makes it more likely some will feel the need to call him as a witness."