At least five and as many as eight more Australian fighters have been killed in Iraq and Syria, taking the toll of the country's recruits to Islamic State to a third of those who have joined the Middle East conflict. 
Foreign Minister Julie Bishop told The Australian yesterday that at least 40, and possibly as many as 43, are believed to have been killed fighting for Daesh, almost one Australian killed a week since   June.
"The number of foreign terrorist fighters joining the conflict in Syria and Iraq continues to grow," Ms Bishop said.
"The government is committed to starving Daesh of the foreign fighters it needs for propaganda and recruitment." Australian Strategic Policy Institute executive director Peter Jennings said Australian recruits were being used as "cannon fodder" for the movement as the conflict escalated.
"They are most likely to have been killed either in combat or as suicide bombers," Mr Jennings told The Australian.
"The younger ones are used as suicide bombers because they don't have basic battlefield skills so they are wrapped in explosives." The significant upward revision of the figures - from 35 in   July - could also indicate an intensification of the conflict, he said.
"The last three months or so fighting has been intense and is still continuing, and the sense that Islamic State is being contained is largely not true." About 110 Australian citizens are in Iraq and Syria, and the government has cancelled 140 passports of those seeking to join the conflict. A further 21 passport applications have been denied and 26 suspended.
Deakin University terrorism expert Greg Barton said that many foreign fighters without skills were sent into combat, while protecting those such as prominent Islamic State recruiter, Australian Neil Prakash. "Someone like Neil Prakash has value in propaganda and recruitment," he said.
Professor Barton said the organisation was relying heavily on suicide bombers, in "devastatingly effective" vehicle improvised explosive devices.
At a Senate estimates committee hearing yesterday Australian Defence Force chief Mark Binskin said the Islamic State terror group was increasingly using trucks packed with explosives and driven by suicide bombers to spearhead its attacks.
These so-called "vehicle-borne improvised explosive devices" were often followed by smaller vehicles filled with bombs, Air Chief Marshal Binskin said.
He believed the morale of IS fighters had suffered as a result of the coalition air campaign "because every time they put a head up they get a bomb on it".
Air Chief Marshal Binskin said the number of RAAF missions over Syria had not been reduced since the Russian campaign began.He said a new agreement, signed by the US and Russia, set out guidelines so that each nation's aircraft could stay out of the other's way.