ABC chair Ita Buttrose has a "grave concern" about this week's Australian Federal Police (AFP) raid at the national broadcaster, which she says was "clearly designed to intimidate".

Key points: Ms Buttrose said she had a "frank conversation" with the Federal Communications Minister about the raid

Ms Buttrose said she had a "frank conversation" with the Federal Communications Minister about the raid She said: "As ABC chair, I will fight any attempts to muzzle the national broadcaster."

She said: "As ABC chair, I will fight any attempts to muzzle the national broadcaster." Wednesday's raid at the ABC's Sydney headquarters lasted more than eight hours

AFP officers executed a search warrant at the ABC's Ultimo headquarters on Wednesday, over a series of 2017 stories known as the Afghan Files.

In a statement, Ms Buttrose said she had a "frank conversation" with Federal Communications Minister Paul Fletcher on Thursday, and that the raid was "clearly designed to intimidate".

The AFP also raided the Canberra home of a News Corp journalist on Tuesday — however that incident was not related to the ABC search warrant.

"It is impossible to ignore the seismic nature of this week's events: raids on two separate media outfits on consecutive days is a blunt signal of adverse consequences for news organisations who make life uncomfortable for policy makers and regulators by shining lights in dark corners and holding the powerful to account," Ms Buttrose said.

"I also asked for assurances that the ABC not be subject to future raids of this sort.

"Mr Fletcher declined to provide such assurances, while noting the 'substantial concern' registered by the Corporation."

Prime Minister Scott Morrison said he anticipated Ms Buttrose would raise the issue with him when they next met.

"Ita always said she'd speak her mind, and that's why I picked her, and that's why the Cabinet endorsed that, because she is someone who will speak her mind," Mr Morrison said.

"She's raised these issues and her concerns with the Minister, and I'm sure when we meet which is not too far away she'll reflect similar sentiments.

"But what is important here is two things — the Government is committed to press freedom, of course we are.

"Secondly, the Government is committed to ensure no-one is above the law."

'Independence is not exercised by degrees'

The Afghan Files stories, by ABC investigative journalists Dan Oakes and Sam Clark, revealed allegations of unlawful killings and misconduct by Australian special forces in Afghanistan and were based off hundreds of pages of secret Defence documents leaked to the ABC.

"As ABC chair, I will fight any attempts to muzzle the national broadcaster or interfere with its obligations to the Australian public," Ms Buttrose said.

"Independence is not exercised by degrees. It is absolute."

Ms Buttrose, who is only the second woman to lead the ABC board, said an "untrammelled" media which upholds the community's right to information has driven her journalistic career for almost five decades.

"In my view, legitimate journalistic endeavours that expose flawed decision-making or matters that policy makers and public servants would simply prefer were secret, should not automatically and conveniently be classed as issues of national security," she said.

Ms Buttrose described the search warrant, which named Oakes, Clark and the ABC's Director of News Gaven Morris, as "sweeping".

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 41 seconds 41 s Scott Morrison said he selected Ita Buttrose as ABC chair because she speaks her mind.

Mr Morrison, who previously defended the raid, said it was important to allow the AFP to continue its work professionally.

"There's a process that's underway," he said.

"Let's just allow the AFP to continue its investigations ... we need to allow this process to run to its conclusion."

The raid sparked a global conversation about the public's right to know, with many expressing concern over threats to press freedom and democracy.

The New York Times published an article addressing the raids with the headline "Australia May Well Be the World's Most Secretive Democracy".

After the raid, that lasted more than eight hours, the AFP officers took with them two USB drives containing a small number of electronic files, which were sealed in plastic bags pending a review by ABC lawyers.

The ABC has two weeks to challenge the terms of the warrant as well as claim privilege over the contents of the documents before the AFP can unseal that bag and, potentially, use the files as evidence.

Managing director David Anderson said ABC journalists' sources were safe.