A video appearing to show former South Australian opposition leader David Speirs snorting a substance from a plate should be reported to “the appropriate authorities” if it is a deepfake, Liberal leader Vincent Tarzia says.

Speirs, who quit the leadership a month ago, denies he’s the person in a video and a picture published by News Corp.

He said the person in the video was “certainly not me” and called the footage “very troubling”.

“I believe this is a deep fake or an elaborate hoax,” he said on Tuesday.

Tarzia said the video was “a matter for Mr Speirs, and if it is fake, Mr Speirs should refer it to the appropriate authorities”.

“Any suggestion of this kind of activity is of concern to me, and my party takes these matters very seriously,” he said.

“It would be inappropriate for further comment until all facts are known.”

Tarzia won a partyroom ballot in August after Speirs stepped down, saying he’d “had a gutful” and didn’t have the energy to continue as Liberal leader.

The Advertiser reported the video was recorded at 4.12am on June 30, while Speirs was still party leader, in the kitchen of his Kingston Park home in Adelaide’s southern suburbs.

In a still image, Speirs is captured at the same bench next to a plate with seven lines of white powder. The Advertiser said metadata showed that the image was taken at 6.32am.

The Liberal MP said he “would never have done that” and was “quite horrified”.

The newspaper did not cite a source for the video and image but said it had been obtained after it was passed to a third party.

Premier Peter Malinauskas said deepfakes were “a threat to democracy”.

“The issue of AI-generated images and deep fakes is a challenge that we’ve got to confront, and it’s not unrelated to the social media challenge,” he told Sky News.

“It does represent a threat to democracy. We’re going to keep our eye on it and here in the state parliament we’re actually bringing in legislation to address it and make sure it’s a criminal offence.”

Later he said the images were “quite concerning”.

“But they are a matter exclusively for Vincent Tarzia and the South Australia division of the Liberal Party. The dysfunction, the division, the chaos, that’s a matter for Vincent Tarzia and the Liberal Party,” he said.

Speirs returned to SA last week after a trip to Scotland for a family wedding.

He said he was surprised he was not named in Tarzia’s shadow cabinet and had not yet decided if he would recontest his seat of Black at next year’s state election.

-with AAP