Australia captain Steve Smith must be immediately removed from his role over the ball-tampering row in South Africa, an Australian government agency says.

Smith said on Saturday that the team's "leadership group" had spoken about a plan to tamper with the ball, carried out by batsman Cameron Bancroft.

The Australian Sports Commission (ASC) has now called for Smith "to be stood down immediately, along with any other members of the team leadership group or coaching staff who had prior awareness of, or involvement in, the plan".

The incident took place on the third day of the third Test between South Africa and Australia in Cape Town - escalating the tension around what has been an ill-tempered series.

The ASC statement added: "This [Smith's removal] can occur while Cricket Australia completes a full investigation. The ASC condemns cheating of any form in sport. The ASC expects and requires that Australian teams and athletes demonstrate unimpeachable integrity in representing our country."

Earlier, Cricket Australia (CA) chief executive officer James Sutherland announced that such an investigation would now take place - with CA's head of integrity Iain Roy and head of team performance Pat Howard travelling to South Africa to "gather relevant information" - but that Smith would remain as skipper for now.

Australia captain Steve Smith and vice-captain David Warner step down for rest of Test

Australia captain Steve Smith and vice-captain David Warner have stepped down from their positions for the rest of the third Test against South Africa a day after admitting to ball tampering.

Smith said on Saturday that the team's "leadership group" had spoken about a plan to tamper with the ball, carried out by batsman Cameron Bancroft.

Tim Paine will be captain for the rest of the match, although Smith and Warner will continue to play.

The match is into its fourth day.

"This Test match needs to proceed, and in the interim we will continue to investigate this matter with the urgency that it demands," said Cricket Australia chief James Sutherland.

"Cricket Australia and Australian cricket fans expect certain standards of conduct from cricketers representing our country, and on this occasion these standards have not been met.

"All Australians, like us, want answers and we will keep you updated on our findings, as a matter of priority,"

Prime Minister 'shocked and disappointed'

Less than 24 hours after Bancroft was caught by the cameras taking what he said was yellow tape out of his trouser pocket before rubbing the ball, the row had escalated enough for Australian Prime Minister Malcolm Turnbull to speak out about the issue.

"I am shocked and bitterly disappointed by the news from South Africa," said Turnbull.

"It seems beyond belief the Australian cricket team have been involved in cheating. Our cricketers are role models and cricket is synonymous with fair play. How can our team be engaged in cheating like this? It beggars belief."

Turnbull later added: "I have spoken with David Peever, the chairman of Cricket Australia, and I have expressed to him very clearly and unequivocally my disappointment and concern. He has said to me that Cricket Australia will be responding decisively, as they should.

"It's their responsibility to deal with it, but I have to say that the whole nation, who hold those who wear the baggy green up on a pedestal - about as high as you can get in Australia, certainly higher than any politician, that's for sure - this is a shocking disappointment."

Former players condemn 'premeditated cheating'

Michael Clarke, Smith's immediate predecessor as Test captain, called it "a terrible day for Australian cricket", described the plan as "premeditated cheating" and condemned its instigators for choosing rookie batsman Bancroft to carry it out.

"I can't believe the leadership group have got a young kid playing in his eighth Test match to do this," Clarke told Australia's Channel Nine.

"We have got the best bowling attack in the world. We don't need to cheat to beat anyone."

Clarke retired from international cricket in 2015 after suffering with a chronic back problem for many years, but when asked whether he would consider a shock return if Smith were to depart, he replied: "If I was asked by the right people, then I would think about my answer."

Former Test vice-captain Adam Gilchrist told BBC Radio 5 live that he was "stunned and shocked... embarrassed and sad".

The legendary wicketkeeper said: "Australian cricket is the laughing stock of the sporting world.

"I remember being a current player and the last thing you wanted was ex-players putting the boot in, but I have the feeling we have been all really badly let down here.

"The only positive is that they admitted it. We'll get stories now where it will be 'oh, all teams do it, in different levels and different ways'. But it's not bending the spirit of the game, it's going outside the laws. It's not acceptable."