The new rules come after the Defense Department restricted media access inside the Pentagon, forced some outlets to vacate offices in the building and drastically reduced the number of briefings for journalists.

The media policy "gags Pentagon employees" by threatening retaliation against reporters who seek out information that has not been pre-approved for release, the Pentagon Press Association (PPA) said.

AFP said in a statement Tuesday that it "cannot sign up to the terms of the Pentagon document that would require media to acknowledge insufficiently clear new policies that appear to fly in the face of US constitutional principles and of the basic tenets of journalism."

"We shall continue to cover the Pentagon and the US military freely and fairly, as we have done for decades," the agency added.

TV networks ABC, CBS, CNN, Fox and NBC issued a joint statement saying they will not sign the new rules, which would "restrict journalists' ability to keep the nation and the world informed of important national security issues."

Alongside Fox, other conservative outlets the Washington Times and Newsmax are also reportedly refusing to agree to the new policy, which could see a total of some 100 press passes revoked.

The new rules are the latest in a series of moves that restrict journalists' access to information from the Pentagon, the nation's single largest employer with a budget in the hundreds of billions of dollars per year.

The Defense Department announced earlier this year that eight media organizations including the Times, the Washington Post, CNN, NBC and NPR had to vacate their dedicated office spaces in the Pentagon, alleging that there was a need to create room for other -- predominantly conservative -- outlets.

It has also required journalists to be accompanied by official escorts if they go outside a limited number of areas in the Pentagon -- another new restriction on the press.

And it has drastically reduced the number of briefings for journalists -- holding some half a dozen this year, compared to an average of two or more per week under president Joe Biden's administration, which left office in January.

Pentagon chief Pete Hegseth -- a former Fox News host and Army National Guard veteran -- has campaigned against leaks from the Defense Department.

But he was inadvertently involved in the release of sensitive information earlier this year, sharing details about upcoming strikes against Yemen's Huthi rebels in a chat on messaging app Signal to which a journalist had been mistakenly added.

Hegseth has also reportedly used Signal to discuss US strikes on Yemen with his wife and other people not usually involved in such discussions.

His use of Signal has prompted an investigation by the Pentagon inspector general's office.