Ex-CIA chief John Brennan has hit back at President Donald Trump after he ordered his security clearance revoked, citing the Russia inquiry.
In a newspaper on Thursday, Mr Brennan wrote that Mr Trump's campaign had colluded with Moscow to win in 2016.
The withdrawal of his clearance bars a vocal critic from being able to access sensitive government information.
The White House said his move was due to Mr Brennan's "erratic conduct" and "outrageous allegations".
But in an interview with the Wall Street Journal, Mr Trump cited the Department of Justice ongoing inquiry into Russia's alleged efforts to interfere in the 2016 US election.
"It is a sham," Mr Trump told the Wall Street Journal referring to that investigation.
Revoking Mr Brennan's clearance "had to be done", the US president added.
Mr Trump said that Mr Brennan and "these people" from the US intelligence community had "led" the Russia inquiry.
Mr Brennan was director of the CIA when the alleged Kremlin meddling took place and stepped down after Mr Trump won the election.
In a New York Times piece on Thursday, Mr Brennan said the revoking of his security clearance was a politically motivated "attempt to scare into silence" other critics of the president.
"Mr Trump's claims of no collusion are, in a word, hogwash," the former CIA director wrote in the New York Times.
He said it only remained to determine whether criminal conspiracy, obstruction of justice or money laundering had been committed.
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 year, Mr Brennan said the Russia inquiry was "well-founded" because Russians had "brazenly interfered" in the vote.
President Trump has repeatedly denounced the probe as a political "witch hunt".
What did Trump's statement say exactly?
Mr Trump's written statement on Wednesday was dated to 26 July - three days after the White House first proposed the idea.
It said that Mr Brennan's "lying and recent conduct, characterised by increasingly frenzied commentary... facilitates the very aim of our adversaries, which is to sow division and chaos".
The statement added that Mr Trump was also reviewing access to classified information for nine other high-ranking officials, all of whom have criticised the president:
- James Comey, former FBI director
- Sally Yates, former deputy attorney general
- James Clapper, former director of national intelligence
- Michael Hayden, former national security agency director
- Susan Rice, former national security adviser
- Andrew McCabe, former FBI deputy director
- Peter Strzok, former FBI investigator
- Lisa Page, former FBI lawyer
- Bruce Ohr, former associate deputy attorney general
What has the reaction been?
Democratic lawmakers were strident in their criticism.
Virginia Senator Mark Warner said it "smacks of Nixonian-type practices".
Some Republicans praised the move, including Senator Rand Paul who said he "urged the president to do this."
"[Mr Brennan's] behaviour in government and out of it demonstrate why he should not be allowed near classified information," he said in a statement.
Louisiana Senator John Kennedy said Mr Brennan was a "butthead" who had "given the national intelligence community a bad name".
But Senator Susan Collins, a moderate Maine Republican, was more measured.
She said although Mr Brennan was "far too political in his statements", there were no grounds to revoke his clearance "unless there was a disclosure of classified information".
Changing the subject
Analysis by BBC's North America Editor Jon Sopel
John Brennan has been an outspoken critic of the president.
He called Donald Trump treasonous over his meeting with the Russian leader in Helsinki, he has also called him imbecilic and a danger to the US.
Now Donald Trump has had his revenge, revoking the former CIA chief's security clearance - and threatening a number of other national intelligence officials, all of whom have one thing in common: they've also been critical of the president.
But in justifying this move there's been no suggestion that Mr Brennan either leaked classified material or sought to make money from it.
The timing is also noteworthy. The White House has been buffeted for days by claims from a disaffected former adviser to the president.
Closing arguments in the trial of Donald Trump's former campaign manager, Paul Manafort, are also being heard.
The White House briefing where this was announced hadn't been scheduled. It looks like a concerted effort to change the subject.