Islamic State supporters are seducing Australian youth in a process akin to pedophilic grooming, the head of the country’s security agency warns.

ASIO Director-General of Security Duncan Lewis on Friday said there were about 120 young Australians currently fighting with the extremist group in Syria and Iraq, with others radicalised through “insidious” online manipulation.

“They are being groomed with a technique that is not dissimilar to child molestation,” he told a luncheon in Brisbane.

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“The passage to radicalisation, astonishingly, can happen quite quickly.”

He confirmed 32 citizens had already died in the Middle East with the high number of young people fighting for ISIS in Syria and Iraq “cutting new territory” for Australian society.

It was “heart-breaking” that children as young as 14 were being targeted, he said.

In a wide-ranging speech, Mr Lewis nominated terrorism as ASIO’s “issue du jour” and said Australian society was managing a significant risk.

Notably, he said ASIO had just over 400 high-priority terrorist investigations underway – double last year’s tally.

“So business is brisk,” he quipped.

In particular, Mr Lewis cited the Daesh fighters’ evangelical brand of fundamentalism used to recruit followers and direct attacks on the West.

He also revealed a further 170 ISIS supporters were living in Australia and some 135 passports had been cancelled to stop young locals heading to overseas battle fronts.

These measures were necessary to ensure Australia didn’t export its problems offshore, or see skilled-up fighters return to carry out sophisticated domestic attacks, he said.

Mr Lewis said the 2000-odd strong organisation had recently received a funding boost but was suffering a lag partly because it takes months to carry out security clearances on new staff.

“The kind of thing that worries me is to make sure that we are doing everything we possible can to minimise the risk,” he concluded.

“(But) at the end of the day, we’re still carrying some.”

– AAP