President Donald Trump has been branded a “disgraced demagogue” by former CIA director John Brennan following the sacking of FBI deputy director Andrew McCabe, as Mr Trump’s feud with the bureau shows few signs of abating.

Mr McCabe said after his dismissal, which came just two days before he was due to retire and claim a number of government pension benefits, was the result of him being a crucial witness regarding whether Mr Trump obstructed a federal investigation into possible collusion by members of with Russia.

Mr Trump had welcomed the dismissal of Mr McCabe – who he has frequently taunted both publicly and in private – as “a great day for democracy,” which led to the rebuke by Mr Brennan.

Attorney General Jeff Sessions said late on Friday that he felt justified in firing Mr McCabe after the Justice Department’s internal watchdog said in a report – the contents of which have not yet been made public – that he leaked information to reporters and misled investigators about his actions.

Mr Sessions said Mr McCabe had “made an unauthorised disclosure to the news media and lacked candour – including under oath – on multiple occasions”.

“The FBI expects every employee to adhere to the highest standards of honesty, integrity and accountability,” Mr Sessions added.

Mr McCabe has denied these allegations and called his firing part of a concerted effort by the Trump administration to discredit the FBI. “This attack on my credibility is one part of a larger effort not just to slander me personally, but to taint the FBI, law enforcement, and intelligence professionals more generally,” McCabe said. “It is part of this Administration’s ongoing war on the FBI and the efforts of the Special Counsel investigation.”

The investigation that Mr McCabe referred to is the federal probe being run by Special Counsel Robert Mueller into Russia’s meddling in the 2016 presidential election and possible collusion between Russia and members of Mr Trump’s campaign team. Mr Trump and the White House have denied there was any collusion. The investigation into election meddling was originally led by former FBI Director James Comey before he himself was fired by Mr Trump in May last year.

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Mr Comey later testified to a congressional panel that he had had conversations with Mr Trump where the president had asked him to think about dropping an investigation into the conduct of Mr Trump’s then-National Security Adviser Michael Flynn. The White House have denied such conversations taking place, although it is believed that Mr Mueller and his team are looking into whether Mr Comey’s firing could amount to obstruction of justice. Mr Flynn has since pleaded guilty to one count lying to the FBI, having been indicted by Mr Mueller.

In his statement, Mr McCabe alleged that the report used as the basis for his firing was sped up “only after” his testimony suggested that he would corroborate Mr Comey’s accounts of his conversations with Mr Trump. A source told the Associated Press that Mr McCabe had kept personal memos regarding interactions with the president. They are said to be similar to the ones maintained by Mr Comey.

In his tweet, Mr Trump also used the opportunity to attacked Mr Comey as “sanctimonious” and called Mr McCabe’s firing “a great day for the hard working men and women of the FBI.” He asserted without elaboration that `Mr McCabe “knew all about the lies and corruption going on at the highest levels of the FBI.”

Responding to that, Mr Brennan, who led the CIA under President Barack Obama between 2013 and 2017, made his feelings clear about the reasons for Mr McCabe’s firing by tweeting about Mr Trump: “When the full extent of your venality, moral turpitude, and political corruption becomes known, you will take your rightful place as a disgraced demagogue in the dustbin of history.”

Andrew McCabe FIRED, a great day for the hard working men and women of the FBI – A great day for Democracy. Sanctimonious James Comey was his boss and made McCabe look like a choirboy. He knew all about the lies and corruption going on at the highest levels of the FBI! — Donald J. Trump (@realDonaldTrump) March 17, 2018

When the full extent of your venality, moral turpitude, and political corruption becomes known, you will take your rightful place as a disgraced demagogue in the dustbin of history. You may scapegoat Andy McCabe, but you will not destroy America...America will triumph over you. https://t.co/uKppoDbduj — John O. Brennan (@JohnBrennan) March 17, 2018

“You may scapegoat Andy McCabe, but you will not destroy America... America will triumph over you,” Mr Brennan’s tweet continued.

The former CIA director has previously described the President as “unstable, inept, inexperienced and unethical”.

Mr McCabe briefly served as director of the FBI between the firing of Mr Comey and the swearing-in of current director Christopher Wray. He played a crucial role in the bureau’s investigation into of Hillary Clinton’s use of a personal email server while she was Secretary of State, as well the Clinton Foundation. That is in addition to playing a key role in the probe into Russia’s interference in the election.

Mr McCabe had been on leave from the FBI since January, when he abruptly left the deputy director position, with his subsequent dismissal putting his ability to collect his pension following 20 years of service at the bureau at risk. His removal will likely add to the turmoil surrounding the bureau’s relationship with the Trump administration.

Mr McCabe came under scrutiny over an October 2016 news report about clashes between the FBI and the Department of Justice about about how aggressively the Clinton Foundation should be investigated. The watchdog office concluded that McCabe authorised FBI officials to speak to a Wall Street Journal reporter for that story and had kept back information about it.

In his statement, Mr McCabe said he had the authority to share information with journalists through the public affairs office and that he had honestly answered questions about whom he had spoken to and when, and that when he thought his answers were misunderstood, he contacted investigators to correct them.

At the time, Mr McCabe was faced questions of partisanship, and both then and since he has been repeatedly been criticised by Mr Trump for being biased in favour of Hillary Clinton and because his wife Jill ran as a Democratic candidate for the Virginia State Senate. Ms McCabe had received campaign contributions from the political action committee of then-Virginia Governor Terry McAuliffe, a longtime Clinton friend, during her unsuccessful run. The FBI has said Mr McCabe received the necessary ethics approval about his wife’s candidacy and was not supervising the Clinton investigation at the time.

Mr McCabe suggested in his statement that he was trying to “set the record straight” about the FBI’s independence against the background of those allegations.

Mr Sessions faced a difficult decision over the firing. He risked inflaming the White House if he decided against dismissing Mr McCabe, but the timing of his forced departure is likely to upset ran-and-file members of the FBI.

The firing comes amid of number of resignations or firings of Trump administration staff in the past few weeks, including Secretary of State Rex Tillerson, Mr Trump’s economic adviser Gary Cohn and White House communications director Hope Hicks.

Associated Press contributed to this report