CNN, MS Now, Politico sue Donald Trump over White House ban, show court records

"This ban could not be a more direct assault on the First Amendment nor a more blatant violation of our most fundamental constitutional principles," the media outlets said.

The three news organisations earlier in the day said they had notified the government that they were filing their lawsuit in the US District Court for the District of Columbia and could see emergency hearings in the case as soon as this week. "Without notice or process, the White House revoked our journalists' credentials because it objected to our reporting.

Left unchallenged, this threatens press freedom and the public's right to independent journalism free from government interference," they wrote in a joint statement. The lawsuit aims "to protect our First Amendment rights and defend the principle that the government does not decide what the press reports or publishes," they added.

Representatives for the White House did not respond to a request for comment. Trump defended the ban in another social media post on Monday after the lawsuit was announced, calling the news media a security threat, without providing any evidence.

"The White House is not instituting an assault on the Free Press, something which I cherish. It is instituting an assault on the FAKE NEWS," he wrote. "It is corrupt, purposeful, pervasive, fully coordinated, and totally out of control.

It is a threat to our National Security, and must be stopped, NOW!"The Trump administration has upended decades of tradition in dealings between the White House and press, denying the access many major news organisations have had to the president while elevating new media outlets seen as more sympathetic to the administration.

He has also filed a number of lawsuits against news organisations. Trump's latest move comes as his fellow Republicans seek to defend their narrow majorities in Congress in the November midterm elections as polls show the public souring on Republicans and Trump's own approval ratings stand near historic lows.

On Saturday, all three outlets said their journalists were turned away from the White House grounds and their press credentials confiscated, a day after Trump initially announced his ban in a social media post and threatened to block other outlets.

He later addressed what he called his "ban on the free press" with reporters at an event in the Oval Office and said there was no particular incident that provoked the move.

Asked what other news organisations could be targeted, Trump cited The New York Times and The Washington Post as "fake news" but said they had not been removed yet. The Associated Press, the White House Correspondents' Association and others have criticised Trump's ban, citing the fundamental American right to free speech and calling for access to be immediately restored.

The Associated Press filed its own lawsuit after being barred along with Reuters last year from the group of reporters that cover the president's daily movements.