Former FBI Director James Comey on Thursday slammed the White House's explanations for his firing last month and its criticism of the FBI that followed.

Comey said that the White House "chose to defame" him and the FBI, alleging that the bureau is in "disarray."

"Those were lies, plain and simple. And I am so sorry that the FBI workforce had to hear them, and I'm so sorry that the American people were told them " Comey told the Senate Intelligence Committee.

President Donald Trump abruptly fired Comey last month. The ouster came as he oversaw the FBI's investigation into Russian interference in the 2016 election and possible ties between the Trump campaign and the Kremlin.

Comey said that the White House's "shifting explanations" for Trump firing him "confused and increasingly concerned" him.

The former FBI director said he was concerned by Trump's admission in an NBC interview that he was thinking of the "Russia thing" when he fired Comey. Comey flatly replied "yes" when asked if he thought Trump fired him because of the Russia probe.

"I take the president at his word that I was fired because of the Russia investigation," Comey said, while noting that he "could be wrong."

The former FBI chief said he was confused because Trump had told him that he hoped he would stay on the job. Comey started a 10-year term in 2013.

The White House's explanation that Comey was fired because of his decisions during the election year also baffled Comey because of "the time and the water that had gone under the bridge" since those events happened.