A 17-year-old Australian boy has appeared in an Isis propaganda video, where he warns the UK, US and Australia that militants will keep fighting until "the black flag' is flying over the White House and Buckingham Palace. The video is believed to show Abdullah Elmir, who went missing from his home in Sydney at the end of June. In the footage the teenager can be seen directly addressing the Australian Prime Minister Tony Abbott and US President Barack Obama. He says: "To the leaders, to Obama, to Tony Abbott I say this; these weapons that we have, these soldiers, we will not stop fighting, we will not put down our weapons until we reach your lands, until we take the head of every tyrant and until the black flag is flying high in every single land. Until we put the black flag on top of Buckingham Palace, until we put the black flag on top of the White House, we will not stop, and we will keep on fighting."