Former prime minister John Howard says the conduct of a few special forces personnel in Afghanistan was "totally at odds with the values, beliefs and practices" of Australia's military forces.
Mr Howard as prime minister committed Australian forces to Afghanistan in 2001, following the September 11 terrorist attacks.
During the conflict, 41 Australian Defence Force members died, for which the nation should be grateful, he said.
"None of this diminishes the distress that I and so many others feel about the contents of the Brereton inquiry," Mr Howard said in a statement on Friday.
"Its findings are damning of the behaviour of a small group of special forces personnel who it is claimed, amongst other things, were responsible for the unlawful killing of 39 Afghani citizens.
"The report explicitly states that none of them lost their lives in the heat of battle. Such conduct is totally at odds with the values, beliefs and practices of our military forces."
He said due process must now be followed.
"If charges are laid against individuals they must be handled in accordance with Australia's criminal justice system," Mr Howard said.
"Any personnel charged should enjoy the presumption of innocence.
"A long road lies ahead. In the meantime, we should remember the continuing service of our military personnel and, where appropriate, extend a helping hand to them and their families."
The four-year investigation by Inspector-General of the Australian Defence Force, Paul Brereton, found credible evidence of 23 incidents in which a total of 39 Afghan nationals were unlawfully killed.
The inquiry has recommended the chief of defence refer 36 matters to the Australian Federal Police for criminal investigation, involving 19 individuals.
Former prime minister Kevin Rudd compared the behaviour to that of the Abu Ghraib torture and prison abuse scandal.
"It beggars belief that following the atrocities witnessed during the Iraq war at Abu Ghraib that such crimes could be repeated, and worse, by Australian forces in Afghanistan," he said in a statement.
Australian Associated Press