The horrifying image of a young Australian boy supposedly holding a severed Syrian's head has turned the stomach of US Secretary of State John Kerry.

The image was posted to Twitter and went viral but has since been removed from the social networking site.

The picture was posted by convicted terrorist Khaled Sharrouf and reportedly showed his 7-year-old son clutching a severed man's head in the Syrian city of Raqqa.

Alongside the image was the caption: "That's my boy."

The image has stunned world leaders.

"This image, perhaps even an iconic photograph... really one of the most disturbing, stomach-turning, grotesque photographs ever displayed," Kerry was quoted as saying by The Associated Press.

Australian Prime Minister Tony Abbott told ABC Radio that the image showed "the kind of hideous atrocities that this group is capable of".

According to Stuff.co.nz, Australian-born Sharrouf used his brother's passport to dodge a travel ban and travel to Syria.

The ban had been imposed on him in Australia following his release from prison where he had been serving a five-year sentence on terror-related charges.

According to court documents relating to the terror charges, Sharrouf had a turbulent adolescence, being expelled from school in Year 9 for violent behaviour, and taking drugs, KDVR.com reports. He was also reported to have schizophrenia.

Sharrouf has posted more than one frightening image to the web. Another shows what are believed to be three of his children dressed in camouflage and holding weapons.