Khaled Sharrouf captioned a picture of his young son using both hands to hold up the decapitated head with: 'That's my boy.'

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The Australian national is one of the country's most-wanted terrorists and a suspected war criminal, who is currently fighting in Syria with ISIS.

In the shocking image, the polo shirt clad boy can be seen brandishing his father's kill, clearly uncomfortable with the situation.

Other posts from Sharrouf's Twitter include a picture of him and three of his children, wielding machine guns and wearing camouflage.

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The Australian has directly threatened Aussie journalists on social media, and made it clear that he wants to bring his message of hate back to the country.

Former chief of the Australian Army, Peter Leahy, said that he couldn't 'imagine what this young boy is thinking and I certainly can't imagine what his father's thinking.'

Australian Muslim leaders also slammed the photographs, saying they were working hard to stop the supply of young Muslims to radical groups such as ISIS.