A lengthy investigation into possible war crimes committed by elite Australian soldiers in Afghanistan will not be made public before this year's federal election.

Key points: The war crimes inquiry is set to run on for months, at least until the second half of 2019

The war crimes inquiry is set to run on for months, at least until the second half of 2019 One veteran says those subject to the inquiry are suffering "natural justice impacts"

One veteran says those subject to the inquiry are suffering "natural justice impacts" The Defence Department claims the need for thoroughness and fairness has affected the timeframe

Senior military and government figures have told the ABC they are not expecting the long-awaited report by the Inspector-General of the Australian Defence Force (IGADF) to be ready for release until at least the second half of this year, well after voters go to the polls in May.

In 2016 the IGADF began examining "rumours of possible breaches of the Laws of Armed Conflict by members of the Australian Defence Force", but inside the special forces community frustration is growing at how long the process is taking.

One special forces veteran, speaking on the condition of anonymity, told the ABC that there were "natural justice impacts" from having the inquiry extended, and that it was "painful" for those involved.

"I can only hope the ultimate findings are of sufficient gravity to justify this extended process," the former high-ranking Commando said.

For almost three years New South Wales Supreme Court Justice and Army Reserve Major General Paul Brereton has been leading the secretive IGADF investigation, which is believed to have uncovered numerous concerns about the conduct of elite soldiers, including several incidents of possible unlawful killings.

Many in the ADF had originally anticipated the inquiry would be completed by 2018, but in a statement to the ABC the Defence Department has confirmed the independent IGADF inquiry is "ongoing".

"The timeframe for completion of the inquiry is influenced by the number and complexity of lines of inquiry, the number and location of witnesses and above all the need for thoroughness and fairness," the department said.

"The inquiry is very conscious of the need to finalise its work, and is proceeding as expeditiously as possible, consistent with those constraints."

Neil James from the Australia Defence Association said he was surprised at the length of the inquiry but was pleased to know the findings would not be made public during an election campaign.

"It means that the investigation won't be a distraction from the election, and the election won't be a distraction from the investigation," Mr James said.

However Mr James has also acknowledged the drawn-out process is having a negative effect on members of the elite SAS and Commando units.

"It's a burden for the individuals, quite frankly it's also a burden for the morale of the units, and the sooner the whole country can resolve this issue and the units concerned can get it behind them the better."

The ABC has also approached Defence Minister Christopher Pyne for comment.