Reports said that Caner Temel, 22, was killed on the frontline in January after travelling to Syria to fight in the civil war, joining up with the Islamic State of Iraq and the Levant (ISIL) radical jihadist group.
"From his name and from the photograph that the media showed, that matched the name and a photograph we had of a young soldier who served three years ago," Assistant Defence Minister Stuart Robert told the Australian Broadcasting Corporation.
Robert said Temel would have done basic training, including construction work, arms training and a limited amount of explosives work.
He said Temel's reasons for leaving the Australian military were unclear, nor was it known when he went to Syria or whether he was a dual passport holder.
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But Robert said the case highlighted concerns the government has about the prospect of Australians travelling to Syria to fight in the three-year conflict, which has left more than 130,000 dead.
"If reports are correct - and some commentators are speaking of up to 100 Australian citizens who've chosen to join the fight in Syria - that is a concern because it's clearly a criminal act if you go and serve with a foreign military."
"At present the (defence) department has no knowledge of any other serving military personnel from Australia who are over in Syria fighting," he added.
In January, Australia's government expressed concern at the growing numbers of its citizens travelling to Syria to fight alongside rebel groups, with several reported deaths.
ISIL fighters have fought Syria's regime but have been increasingly battling a coalition of moderate and Islamist rebels angered by their abuses of rival fighters and civilians.