Donald Trump has revoked the security clearance of former CIA director John Brennan - one of his most vocal critics on national security issues.
Announcing the decision Sarah Sanders, the press secretary, accused the former intelligence chief of "erratic conduct and behaviour", adding he had "leveraged" his security status to make "unfounded, outrageous" allegations about the administration.
"Mr Brennan has a history that calls into question his objectivity and credibility," she added.
The former intelligence chief reacted by saying he would not back down.
"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," he said.
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
Last month he called the US president's performance at a joint press conference with Russian President Vladimir Putin in Finland "nothing short of treasonous."
This week Mr Brennan levelled a blistering attack against Mr Trump for the president's tweeted criticism of former White House aide Omarosa Manigault Newman, who wrote a book critical of Trump.
"It’s astounding how often you fail to live up to minimum standards of decency, civility, & probity. Seems like you will never understand what it means to be president, nor what it takes to be a good, decent, & honest person. So disheartening, so dangerous for our Nation," Mr Brennan wrote.
Ms Sanders said the security clearance of other former intelligence officials, including James Clapper, the former director of national intelligence, and ex-FBI director James Comey were also "under review".
Former intelligence officials usually keep their security clearance but rarely use it, sometimes providing advice to successors.
The other officials whose clearances are being reviewed are former CIA director Michael Hayden, former national security adviser Susan Rice, and Andrew McCabe, who served as Trump's deputy FBI director until he was fired in March.
Peter Strzok, a fired FBI agent, FBI lawyer Lisa Page and senior Justice Department official Bruce Ohr were also named as under consideration.
Democratic members of Congress said it smacked of an "enemies list" among fellow Americans and the behaviour of leaders in "dictatorships, not democracies."
House Minority Leader Nancy Pelosi slammed the move as a "stunning abuse of power."
Revoking the security clearance of an honorable patriot is a stunning abuse of power & a pathetic attempt to silence critics. This is yet another disturbing attempt by @realdonaldtrump to distract & divert attention from his Admin's #cultureofcorruption, cronyism & incompetence.— Nancy Pelosi (@NancyPelosi) August 15, 2018
Sen. Mark Warner of Virginia, the top Democrat on the Senate intelligence committee, warned that a "dangerous precedent" was being set by "politicising the way we guard our national secrets just to punish the president's critics."
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.— Adam Schiff (@RepAdamSchiff) August 15, 2018
An enemies list is ugly, undemocratic and un-American. I also believe this action to silence a critic is unlawful. https://t.co/bfOhThIWfq
Several Republicans also weighed in, with Sen. Bob Corker saying: "Unless there's something tangible that I'm unaware of, it just, as I've said before, feels like a banana republic kind of thing."
In a phone interview with MSNBC, Mr Brennan called the move an "abuse of power by Mr. Trump."
"I do believe that Mr. Trump decided to take this action, as he's done with others, to try to intimidate and suppress any criticism of him or his administration," he said, adding that he would not be deterred from speaking out.
Trump's action, critics and nonpartisan experts said, marked an unprecedented politicization of the federal government's security clearance process. It also was a clear escalation in Trump's battle with members of the U.S. intelligence community as the investigation into Russia election meddling and possible collusion and obstruction of justice continues.
At least two of the former officials, Mr Comey and Mr McCabe, have said they do not currently hold security clearances.
Mr Trump's former national security adviser Michael Flynn, who has pleaded guilty to lying to the FBI, was not on the list.
It is understood that Mr Trump's current director of national intelligence, Dan Coats, was not consulted on the decision to revoke Mr Brennan's clearance.
At the time, the White House accused them of "politicising and in some cases monetising their public service and security clearances" to make "baseless accusations" against the president.
In response Mr Clapper described it as a "a very, very petty thing to do".
"The president has that prerogative, but if he chooses to do it for political reasons I think that's a terrible precedent. It's petty retribution for speaking out against the president."