Foreign Minister Julie Bishop says intelligence agencies would look closely at the Seven Network video shown on Friday featuring the man, identified as Abu Ousama.
Ousama is described as Australian born but part of the Jund al Aqsa rebel group, made up largely of foreign fighters, who are operating in Syria.
"You have these beheadings and some people might call them barbaric," Ousama, who says he is a combat medic, told British photojournalist Tam Hussein.
"... but what is the difference between a missile that hits a house which kills 15 kids compared to a man dying getting cut by his throat."
He did not rule out fighting against Australian forces.
"I hope Allah sees the good work we've done and blesses us with his reward [of paradise]," he said.
Australian man identified as Abu Ousama, who Channel Seven reports is fighting in Syria as a brigade combat medic. (Screenshot/Channel 7)
Speaking in Hobart on Saturday, Ms Bishop said it was "unfathomable" why Australians would want to take up arms and fight in a conflict on the side of an organisation that exults in beheadings and executions.
"I'm appalled by it," she says.
"It's unthinkable that someone would believe that beheadings are part of a legitimate territorial aspiration. These are murderous cults and they are using Islam to cover up for their violent behaviour.
"This (footage) goes to demonstrate why we're so determined to prevent foreign fighters from Australia taking up arms with terrorist organisations such as ISIL in Iraq and Syria.
"In my mind we need to do all we can to work with communities within Australia, the communities from where these people are coming, so that we can convince them that taking up with terrorist organisations is not only unlawful but it cannot be in their interests."
It is against the law in Australian to fight with a terrorist organisation or support a terrorist organisation, with penalties of to 25 years imprisonment, Ms Bishop says.
Australian man identified as Abu Ousama, who Channel Seven reports is fighting in Syria as a brigade combat medic. (Screenshot/Channel 7)
Australian man identified as Abu Ousama, who Channel Seven reports is fighting in Syria as a brigade combat medic. (Screenshot/Channel 7)
Ousama said he wanted Australians to believe he would pose no risk if he returned to Australia but said he was not afraid to die in Syria.
