The head of ASIO says 50 Australians are confirmed dead serving with the IS group in the Middle East and that appeared to be deterring new recruits.
As many as 59 Australian jihadists have been killed in Iraq and Syria with 50 confirmed dead, the head of ASIO says.
The dead include Neil Prakash, the most senior Australian in Islamic State, and Shadi Jabar, sister of Parramatta shooter Farhad Jabar, who were both killed in separate air strikes in the last week.
Duncan Lewis, director-general of the Australian Security Intelligence Organisation, said 110 Australians were known to be serving with IS in Iraq and Syria, unchanged from earlier estimates.
Also unchanged is the estimate of 190 in Australia supporting IS through funding, recruitment and exhorting others to join the fight in the Middle East or through attacks in Australia.
He said what had been increasing was the number of Australians dying while fighting for or supporting IS, with 50 now confirmed dead in Syria and Iraq. That may include some aged as young as 18.
"That figure may be as high as 59," he told a Senate estimates committee hearing.
As well, passports of 177 Australians planning to travel to the Middle East to join IS have been cancelled. Another 33 were suspended temporarily with most subsequently cancelled.
Mr Lewis said the number of Australians in Syria and Iraq appeared to have reached a plateau for a number of reasons.
It could be that the demographic wishing to go had been exhausted. The community and families were now far more engaged in supporting those who might have sought to travel overseas.
Mr Lewis said the high mortality rate of Australian fighters was probably resonating.
"It wouldn't be difficult to work out that the statistics are not particularly good for young Australians going away. We have said always it is very very dangerous. I think that message has probably got around," he said.
Mr Lewis said he was also encouraged by programs countering violent extremism which now appeared to be gaining traction.