Washington (CNN) Bill Taylor -- the former top US diplomat in Ukraine who served as a key witness in the House impeachment investigation into President Donald Trump -- denounced attacks on former US Ambassador to Ukraine Marie Yovanovitch as "unconscionable" and said that he thought Secretary of State Mike Pompeo was under pressure not to back her.

Speaking exclusively to CNN's Jake Tapper Friday in his first interview since leaving Kiev in early January, Taylor said he "absolutely" believes in Yovanovitch's credibility.

The career diplomat also said it bothered him to see any of his fellow witnesses -- including Yovanovitch and Lt. Col. Alexander Vindman , the Ukraine expert on the National Security Council who was ousted Friday afternoon -- unfairly maligned.

"It of course bothers me any time I see someone like Masha Yovanovitch or Alex Vindman unfairly attacked," Taylor told Tapper.

Taylor added that he believed that Pompeo was "under pressure" not to support Yovanovitch.

"I do believe that he wants to support every member of the State Department, every employee. I do believe he wants to do that," Taylor said. "I also believe he's under some pressure, from other parts of the government, not to support some of the people in the State Department."

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Taylor declined to say whether he believed that pressure came from Trump.

Yovanovitch, who retired last week, was forced out of her her post in Kiev following a targeted smear campaign driven by Trump allies, including his personal lawyer Rudy Giuliani. She was repeatedly maligned by Trump, and recently revealed evidence suggested that she may have been surveilled while in Ukraine.

Taylor was also denounced by the President as a "Never Trumper," a claim that the career foreign service officer emphasized to CNN was false. He called the attacks by Trump "a little weird."

Pompeo has faced heavy criticism for failing to defend the diplomats who came under fire from the President. In a recent interview with NPR, the top US diplomat insisted that he has defended "every State Department official," but failed to cite a specific instance where he had defended Yovanovitch. In an interview with ABC last week, he denied that he felt any "moral tension" about how she had been treated. Yovanovitch, in her public testimony, called on the State Department's leadership to do more to defend its diplomats.

Taylor, who spoke to CNN days after the President was acquitted in his impeachment trial, declined to offer his thoughts on the outcome, saying it was up to voters to decide in November whether Trump's actions warranted his removal from office.

However, the two-time top envoy in Ukraine expressed concern about a potential precedent being set for the withholding of security assistance.

"I have concern about a precedent having been set where we withhold security assistance to a country that is in a fight, is in a battle , is in a war. ... In particular with the Russians, one of our two big adversaries we have identified. So I have very great concern about that and I would be concerned about that in the future," Taylor told CNN Friday. "I am concerned about a withholding of assistance for reasons that are not related to national security."

Taylor testified during the House impeachment inquiry that security aid to Ukraine was withheld as leverage for the Ukrainian government to open an investigation into Trump's political rival, former Vice President Joe Biden and his son, Hunter Biden. Trump and his allies have repeatedly made unfounded and false claims to allege that the Bidens acted corruptly in Ukraine.

Reflecting on all the facts that had come to light in the impeachment process, Taylor said he stood by his testimony.

"I was, as you say, just reporting what I was told what I heard, what people had described to me and that turns out to have been corroborated by most of the other witness," he told Tapper Friday. "And it seems to me that's there's not really a question about the facts of the case and so that made what I said not controversial. It was pretty straightforward."