Elite Australian soldiers forced to give evidence to a secretive inquiry into alleged war crimes in Afghanistan are receiving "comprehensive support services", according to the Defence Department.

Key points: An inquiry into the conduct of special forces in Afghanistan has been underway since 2016

An inquiry into the conduct of special forces in Afghanistan has been underway since 2016 A lawyer for several veterans says the lengthy process is causing harm

A lawyer for several veterans says the lengthy process is causing harm But the Defence Department says the welfare of serving and former ADF members is a "paramount consideration"

Since May 2016 New South Wales Justice Paul Brereton has been assisting the Inspector General of the Australian Defence Force (IGADF) in examining the conduct of special forces personnel during the war in Afghanistan.

Lawyer Glenn Kolomeitz, who has represented several veterans who have given evidence to the IGADF, warns the lengthy process is causing harm.

"None of the blokes I've assisted have had any sort of follow-up enquiries and quite frankly Defence and indeed the IGADF are fully aware that some of these guys are struggling," he said.

Last week commando Kevin Frost, one of Mr Kolomeitz's former clients, took his own life, three years after coming forward publicly with allegations of war crimes in Afghanistan.

"It's one thing for Defence to compel its people before coercive inquiries, but it's quite another to then cut them away without any welfare follow-up, any welfare support," Mr Kolomeitz told the ABC.

However, the Defence Department has rejected suggestions it is abandoning serving and former ADF members who have been compelled to appear before the IGADF's inquiry.

"Welfare continues to be a paramount consideration during the inquiry and we endeavour to ensure current and former serving ADF members and their families have access to comprehensive support services appropriate to their needs, especially those who are vulnerable or at risk," a spokesperson said.

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 Kevin Frost raised allegations of war crimes committed by Australian soldiers, before taking his own life.

"Defence provides comprehensive healthcare including routine and targeted screening for physical and mental health conditions for all ADF members," the spokesperson added.

The Department also defended the long duration of the inquiry, which will soon enter a fourth year.

"The time frame for the IGADF Afghanistan inquiry is influenced by the number and complexity of lines of investigation; the number, location, availability and welfare of witnesses; and above all the need for thoroughness and fairness."

"For all concerned, clarity regarding these serious issues is critical, and therefore the inquiry must be conducted in full and allowed to run its necessary course."

Mr Kolomeitz says he appreciates the difficulties the IGADF is facing while investigating alleged war crimes in Afghanistan, but believes the process is taking too long.

"It's undoubtedly a very complex inquiry, there's no doubt about that. The allegations arise in an operational setting overseas which is still a war zone. But three years is a long time in anyone's books".