General Campbell told Labor senators he was "discomforted" by the use of Defence force footage in the advertisement, which was authorised by Mr Morrison and the Liberal party.

The defence force closely guards its reputation as an apolitical body, and General Campbell said he had offered his advice to the government when the advertisement was first made public.

Posted on Mr Morrison's Facebook page during the summer's bushfire crisis, the video included information about the government's response, including the deploying army reservists and navy ships as part of evacuation efforts.

General Campbell didn't elaborate on the advice he gave to the government on the advertisement, but told the Senate estimates committee he believed changes were made to the advertisement after his conversation with Mr Morrison.

"Whenever the Australian defence force or any other apolitical body finds itself between political parties I am discomforted," General Campbell said.

"And I don't suggest there was intentionality in that circumstance, but the Australian defence force in particular needs to, wherever possible and always be ... nonpartisan both in reality and perception.

"So I am discomforted, but I did not see ill intent in the actions."

The government has disputed the description of the video as an advertisement.

"This was important information communicated to the Australian people," Mr Morrison said in question time.

"I observed the requirements of the Australian Electoral Act that any such videos need a proper authorisation, and that authorisation was provided."

Defence secretary Greg Moriarty said he wasn't asked for permission for the footage to be used, but that there had been discussions between his department and the minister about the video.

Mr Moriarty said he hadn't raised concerns about the footage being used formally.

"Approval was not sought, nor was it given," he said.

Defence Minister Linda Reynolds said permission to use the footage wasn't sought because it wasn't needed.

Canberra Times