A lawyer for the fired FBI deputy director Andrew McCabe said on Friday he was considering filing a defamation lawsuit against Donald Trump and his “colleagues”.

Michael Bromwich – a former justice department inspector general and federal prosecutor – sarcastically thanked Trump in a Twitter post for “providing even more material” for a lawsuit he is considering.

The statement was in response to a Trump tweet that said McCabe “LIED! LIED! LIED”.

Trump’s tweet followed the publication of a harshly critical inspector general report. The report alleged that McCabe improperly authorized the release of information to a newspaper reporter and then misled investigators about it.

The inspector general’s finding led FBI disciplinary officials to recommend that the justice department fire McCabe. The attorney general, Jeff Sessions, dismissed him last month, two days before his scheduled retirement, for what he described as a lack of candor.

McCabe has disputed that assessment and issued a point-by-point rebuttal on Friday. He says that when he believed his answers to the inspector general had been misunderstood, he went back and tried to correct them. In a lengthy statement, Bromwich said the inspector general unfairly tried to conclude its work before McCabe could retire.

Trump commented on the report on Friday afternoon.

“DOJ just issued the McCabe report – which is a total disaster,” the president tweeted, adding: “He LIED! LIED! LIED! McCabe was totally controlled by Comey – McCabe is Comey!! No collusion, all made up by this den of thieves and lowlifes!”

That was a reference to the former FBI director James Comey, whose book about the administration has angered Trump. Copies of A Higher Loyalty were obtained by the Guardian and other outlets on Thursday, five days before publication.

On Friday morning, Trump tweeted that Comey was “a proven LEAKER & LIAR”, a “weak and untruthful slime ball” and “a terrible director of the FBI”.