In the video the boy warns that the movement won't stop fighting until the extremists' notorious black flag is flying in every nation.
Australian media yesterday widely reported a video posted on YouTube in which a speaker believed to be 17-year-old Abdullah Elmir of Sydney warns western leaders of the terror group's resolve.
Using the name Abu Khaled, holding a rifle and dressed in military garb, he is surrounded by dozens of other male jihadists as he addresses the camera.
According to media reports, Abdullah went missing in June, saying he was going fishing.