Sharrouf son used in another IS image

A new photo has surfaced which reportedly shows the youngest son of Australian terrorist Khaled Sharrouf promoting Islamic State.

The image shows the six-year-old standing in front of a man's body tied to a cross and with a sign hanging from his neck which reads: "The Crime: Collaborating with Christians. The Punishment: Execution", according to Seven News.

NSW Police on Sunday confirmed counter-terrorism police were aware of a photo "depicting a minor making threats in the name of ISIS".

"The Joint Counter Terrorism Team is investigating the image, however, there is no specific threat," a police spokeswoman told AAP in a statement.

"The current national terrorism threat level remains at probable," she said.

It's not the first time Sharrouf - who left Australia for the Middle East to become a IS fighter in 2013 - has used his children in this way.

A video featuring the six-year-old wearing a suicide vest and threatening to murder Australians emerged just last week.

Another of Sharrouf's sons - then aged seven - has also been shown in a photograph holding the severed head of a slain soldier.

Sharrouf's wife, Tara Nettleton, died in 2015, leaving their five children in the Middle East.

Nettleton's mother Karen has tried unsuccessfully to bring the children back to Australia.