Donald Trump has revoked former CIA director John Brennan's security clearance, a move he said was about fulfilling his "constitutional responsibility to protect the nation's classified information".

The decision has been seen as an unprecedented act of retribution against a vocal critic of the US president, who hit back in a tweet, saying his principles were "worth far more than clearances", adding: "I will not relent."

President Trump has also threatened to remove clearances from eight former officials and one current official.

Most of the individuals in question are top intelligence officials who also worked under Barack Obama and previous administrations.

Image: Mr Trump cited Mr Brennan's 'erratic conduct' in his statement

Addressing the clearance removal, Mr Trump dismissed Mr Brennan's criticism and cited "the risks posed by his erratic conduct and behaviour".


Democratic congressmen said the president was taking action against those on an "enemies list" and likened his behaviour to leaders in "dictatorships, not democracies".

In a statement, President Trump accused Mr Brennan of having "leveraged his status as a former high-ranking official with access to highly sensitive information to make a series of unfounded and outrageous allegations, wild outbursts on the internet and television about this administration".

It continued: "Mr Brennan's lying and recent conduct characterised by increasingly frenzied commentary is wholly inconsistent with access to the nation's most closely held secrets."

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It comes after the former CIA director hit out at the president over his meeting with Russia's Vladimir Putin last month, calling it "nothing short of treasonous".

Mr Brennan said he learned of the decision only when the White House made an announcement.

He added: "This action is part of a broader effort by Mr Trump to suppress freedom of speech and punish critics.

"It should gravely worry all Americans, including intelligence professionals, about the cost of speaking out."

This action is part of a broader effort by Mr. Trump to suppress freedom of speech & punish critics. It should gravely worry all Americans, including intelligence professionals, about the cost of speaking out. My principles are worth far more than clearances. I will not relent. https://t.co/TNzOxhP9ux — John O. Brennan (@JohnBrennan) August 15, 2018

“John Brennan is a stain on the Country, we deserve better than this.” Former Secret Service Agent and author of new book, “Spygate, the Attempted Sabotage of Donald J. Trump,” Dan Bongino. Thank you Dan, and good luck with the book! — Donald J. Trump (@realDonaldTrump) August 16, 2018

President Trump's statement said Mr Brennan's clearance issue raised wider questions about allowing former officials to keep their security clearances. He said others were under review.

They include former FBI director James Comey, former CIA director Michael Hayden and Andrew McCabe, who worked as deputy FBI director under Mr Trump until he was fired in March.

Currently former CIA directors and other national security officials are allowed to keep their clearances for a period of time so they can advise their successors.

Democratic congressman Adam Schiff, tweeted: "In adding John Brennan to his enemies list, Trump demonstrates again how deeply insecure and vindictive he is - two character flaws dangerous in any president.

"An enemies list is ugly, undemocratic and un-American.

"I also believe this action to silence a critic is unlawful."

Democrat Chris Van Hollen tweeted: "Trump is now categorising dissent and free speech as 'erratic behaviour'... Leaders behave like this in dictatorships, not democracies."