Former soldier-turned-independent senator Jacqui Lambie is demanding a pre-emptive pardon for any defence personnel accused of war crimes against the Taliban or Islamic State.

Her call comes a week after the ABC revealed a secretive Defence review of Australia's special forces has begun hearing allegations of war crimes committed in Afghanistan.

"Would the minister agree that because of the Taliban and Islamic State fighters' subhuman behaviour and vile, disgusting culture and ideology that they should be exempted from any rules of war or international human rights?" Ms Lambie asked Defence Minister Marise Payne at a Senate estimates hearing.

Senator Payne responded by saying the allegations being considered by Defence were serious matters, and the Government wanted to see the outcome of the review.

Already, one serving commando, Kevin Frost, has gone public with his claims that he helped cover up the unlawful execution of a prisoner of war in Afghanistan.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 36 seconds 1 m 36 s Commando speaks about alleged execution of prisoner

Under questioning by senators, Chief of Army Angus Campbell formally confirmed that New South Wales Supreme Court Justice Paul Brereton was helping the ADF's Inspector General to examine the incident and other issues involving the conduct of elite soldiers.

Lieutenant General Campbell told the hearing the special forces review will be a lengthy and independent review, but should be completed within two years.

"There is no time limit, there is no time frame and similarly as you can understand in the discussion we're having I'm being very particular not to make any loose characterisation of rumours, issues, stories that are under inquiry," he said.

Acting Defence Chief Vice Admiral Ray Griggs also took issue with Senator Lambie describing the Inspector General's investigation as a "war crimes inquiry".

"I really think it's unhelpful to keep on calling this a war crimes inquiry. It is not," he said.

"It is a scoping inquiry about the culture of special forces, and every time we use the language we are creating a situation where fewer and fewer people will be open."