WASHINGTON — President Trump on Friday lashed out at the impeachment process and said a key witness — who swore under oath to be truthful — made up his testimony.

In a 53-minute phone interview with “Fox & Friends,” Mr. Trump referred to the account from David Holmes, a political counselor to the American ambassadors in Ukraine, who told impeachment investigators on Thursday that he had overheard Mr. Trump on a phone call with the American ambassador to the European Union ask about investigations into his political rivals.

“I guarantee you that never took place,” Mr. Trump said.

Mr. Holmes on Thursday described in detail the phone call between Mr. Trump and the ambassador, Gordon D. Sondland, discuss a recent meeting with President Volodymyr Zelensky of Ukraine. The two were dining together in a Kyiv restaurant a day after the phone call between Mr. Trump and Mr. Zelensky, which is at the heart of the impeachment investigation.

He addressed other topics during the interview, including the Democratic presidential candidates, progress on the wall along the United States border with Mexico and the pro-democracy protests in Hong Kong.