Australian teenage runaway reportedly appears in Islamic State video warning world leaders

An Australian teenager who ran away from home has reportedly appeared in an Islamic State propaganda video.

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 on Tuesday 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.

Elmir's family could not immediately be reached for comment.