Fox Corp Chairman Rupert Murdoch has acknowledged under oath that some Fox hosts “endorsed” the notion that the 2020 US presidential election was stolen, according to court documents revealed in the US.

Documents unsealed in Delaware State Court on Tuesday morning (AEDT) show Mr Murdoch and other Fox executives believed President Joe Biden fairly beat Donald Trump and that the results were not in doubt, despite the repeated on-air protestations of Fox hosts.

“Some of our commentators were endorsing [the idea that the 2020 election was stolen],” Mr Murdoch told lawyers, when asked about Fox’s hosts’ on-air positions about the election.

The acknowledgement by Mr Murdoch is included in a filing on Monday from Dominion Voting Systems, as part of the voting technology company’s $US1.6 billion ($2.4 billion) defamation lawsuit against Fox News and parent company Fox Corp over Fox’s coverage of the 2020 presidential election.

A five-week trial is scheduled to begin on April 17.

Mr Murdoch’s testimony is part of his deposition in the lawsuit. Parts of it have remained sealed.

Dominion has argued that internal communications and depositions by Fox personnel prove the network knowingly spread falsehoods about Mr Trump’s loss in the 2020 US presidential election in order to bolster its ratings.

Fox has argued that its coverage of claims by Mr Trump’s lawyers were inherently newsworthy and protected by the First Amendment of the US Constitution.

“Executives at all levels of Fox – both (Fox News Network) and (Fox Corporation) – knowingly opened Fox’s airwaves to false conspiracy theories about Dominion,” Dominion wrote in its filing.

Asked by a Dominion lawyer if some of Fox’s commentators had endorsed the idea that the 2020 election was stolen, Mr Murdoch responded:

“Yes. They endorsed,” according to the filing.

“I would have liked us to be stronger in denouncing it, in hindsight,” he said.

The filing also revealed that Mr Murdoch referred to some of Mr Trump’s election lies as “bulls–t and damaging.”

The latest filing by Dominion opposes Fox’s motion for summary judgment. It had sought a ruling that would pre-empt the need for a trial on certain legal issues.

In its own filing made public on Monday, Fox hit back.

“Dominion’s lawsuit has always been more about what will generate headlines than what can withstand legal and factual scrutiny,” the network said.

“[That is] illustrated by them now being forced to slash their fanciful damages demand by more than half a billion dollars after their own expert debunked its implausible claims.”

The Fox documents argued that the media company’s coverage of statements by Mr Trump and his lawyers was inherently newsworthy and that Dominion’s “extreme” interpretation of defamation law would “stop the media in its tracks”.

“Under Dominion’s approach, if the president falsely accused the vice president of plotting to assassinate him, the press would be liable for reporting the newsworthy allegation so long as someone in the newsroom thought it was ludicrous,” Fox said.

Dominion sued Fox News Networks and parent company Fox Corp in March 2021 and November 2021 in Delaware Superior Court, alleging the cable TV network amplified false claims that Dominion voting machines were used to rig the 2020 election against Mr Trump, a Republican who lost to Democratic rival President Biden.

In a statement, a Fox spokesman said Dominion’s view of defamation law “would prevent journalists from basic reporting and their efforts to publicly smear Fox for covering and commenting on allegations by a sitting president of the United States should be recognised for what it is: a blatant violation of the First Amendment”.

Dominion’s motion for summary judgment was replete with emails and statements in which Mr Murdoch and other top Fox executives say the claims made about Dominion on-air were false – part of the voting machine company’s effort to prove the network either knew the statements it aired were false or recklessly disregarded their accuracy.

That is the standard of “actual malice”, which public figures must prove to prevail in a defamation case.

Top legal experts have told CNN that Dominion’s legal position appears strong.

“It’s a major blow,” First Amendment lawyer Floyd Abrams said of Dominion’s motion for a summary judgment.

Harvard Law School professor Rebecca Tushnet said Dominion’s evidence was a “very strong” filing that “clearly lays out the difference between what Fox was saying publicly and what top people at Fox were privately admitting”.

She said she’d never seen such damning evidence collected in the pre-trial phase of a defamation suit.

“I don’t recall anything comparable to this … Donald Trump seems to be very good at generating unprecedented situations,” she told CNN.

-with AAP