Fired FBI Director James Comey on Thursday accused the Trump administration of defaming him and telling "lies" in impassioned testimony before the Senate Intelligence Committee.

The White House's shifting rationale for his dismissal "confused" the former director, he said, adding that it was the administration's subsequent statements that the FBI was in "disarray" that moved him to speak.

"The administration chose to defame me and, more importantly, the FBI by saying that the organization was in disarray, that it was poorly run," Comey told a rapt hearing room.

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"Those were lies, plain and simple."

President Trump last month shocked Washington with his abrupt dismissal of Comey, who was then investigating any coordination between the Trump team and Russia during the campaign.

The White House initially claimed that Comey was fired over his handling of the investigation into Hillary Clinton Hillary Diane Rodham ClintonFox News poll: Biden ahead of Trump in Nevada, Pennsylvania and Ohio Trump, Biden court Black business owners in final election sprint The power of incumbency: How Trump is using the Oval Office to win reelection MORE’s private email server — but Trump himself later told NBC’s Lester Holt that he was thinking of the Russia investigation when he made the decision.

That admission drew the most media attention — but he also told reporters that Comey wasn’t “doing a good job,” a claim a White House spokesperson backed up by arguing that the former director had lost the confidence of the “rank-and-file” at the bureau.

Comey vowed Thursday that he had long believed that as FBI director, he served at the discretion of the president and could be fired “for any reason or for no reason at all.”

But the variety of explanations given for his dismissal “confused me and gave me concern,” he said.

He was confused, he continued, because the president on multiple occasions had assured him he was doing a great job and would remain in the position.

“He told me repeatedly that he had talked to lots of people about me, including the attorney general, and had learned that I was doing a great job and was extremely well-liked by FBI workforce,” Comey said.

Press reports that the president told Russian officials that Comey’s dismissal “relieved great pressure” on him also gave him pause, the former FBI director added.

Comey’s voice was calm and impassive during this portion of testimony, but when he turned to the criticisms of the bureau, he quickly became passionate as the room held its breath.

“I am so sorry that the FBI workforce had to hear that,” he said. “I want the American people to know this truth: The FBI is honest. The FBI is strong and the FBI is and always will be independent.”

Although he was deeply controversial at times, Comey has long been a staunch defender of FBI staff. One of the few times he’s become heated when testifying before Congress was when the integrity of the bureau was questioned.

“You can call us wrong, but don’t call us weasels. We are not weasels,” Comey declared at a House Judiciary Committee hearing in September

He added an emotional message to his former colleagues at Thursday’s hearing.

“To my former colleagues: I am so sorry that I didn’t get the chance to say goodbye to you properly. It was the honor of my life to serve beside you, to be part of the FBI family, and I will miss it for the rest of my life.”

Read more from The Hill:

Live coverage: Comey testifies before Senate Intelligence Committee