A photograph of a child said to be the son of an Australian convicted terrorist holding the severed head of a Syrian soldier has been published in a newspaper.
Prime Minister Tony Abbott told ABC radio that the photograph was further evidence of "just how barbaric" the Islamic State group is.
The Australian newspaper reported that the photograph of terrorist Khaled Sharrouf's son, who was raised in Sydney, was posted on Twitter by his proud father.
"That's my boy!" Sharrouf apparently posted beneath the image that was taken in the northern Syrian city of Raqqa, the capital of what has been declared that an Islamic Caliphate by the Islamic State, the newspaper reported.
The child, who is not named, appears to be younger than 10 years old.
Sharrouf used his brother's passport to leave Australia last year with his wife and three sons to fight in Syria and Iraq. The Australian government had banned him from leaving the country because of the terrorism threat he posed.
He was among nine Muslim men accused in 2007 of stockpiling bomb-making materials and plotting terrorist attacks in Australia's largest cities, Sydney and Melbourne.
He pleaded guilty to terrorism offences and was sentenced in 2009 to four years in prison.
Australian police announced last month that they had arrest warrants for Sharrouf and his companion Mohamed Elomar, another former Sydney resident, for "terrorism-related activity".
They will be arrested if they return to Australia.
The warrants followed photographs being posted on Sharrouf's Twitter account showing Elomar smiling and holding the severed heads of two Syrian soldiers.
In June, The Australian newspaper published a photograph of Sharrouf posing among the bodies of massacred Iraqis.
Mr Abbott, who is in the Netherlands, said he expected Australian C-130 Hercules and C-17 Globemaster military transport planes would join multinational humanitarian efforts this week on Iraq's Sinjar Mountain.
"Australia will gladly join the humanitarian airlifts to the people stranded on Mount Sinjar," he said. "This is a potential humanitarian catastrophe."
He said Islam State's quest for a terrorist nation posed "extraordinary problems" for the Middle East and the wider world.
"We see more and more evidence of just how barbaric this particular entity is," Mr Abbott said.