ASIO boss David Irvine says Australian jihadists have carried out some of the "worst of the worst" extremist atrocities in Syria and Iraq and warns this could inspire young followers at home.

In a speech on Tuesday night, Australia’s top spy, who has adopted an unusually strong public presence in recent weeks as concerns grow about Australians fighting in the Middle East, called the current Middle East conflicts "social media wars".

ASIO boss David Irvine said the conflicts in Syria and Iraq are "creating a new generation of Islamist extremists" much like Afghanistan did in the 1990s. Credit:Alex Ellinghausen

"Extremists use this new media to disseminate their message, interactively bringing their gory barbarity back to Australia, with the aim of radicalising young Australians in real time as they sit at home or wait for buses and trains in the morning," he told the Institute of International Affairs.

Mr Irvine said Australian jihadists such as the now infamous Khaled Sharrouf and Mohamed Elomar, who have been steadily posting gruesome pictures on web social media sites, were serving as “English-language Islamist, extremist propagandists”.