CANBERRA, Feb. 18 (Xinhua) -- The fate of as many as 100 Australians who left the country to fight for Islamic State (IS) remains unknown, the Australian government said.

Of the 230 Australians who travelled to the conflict zone in the Middle East to take up the fight for the jihadist militant group, nearly 100 have been confirmed dead and 40 have returned while a handful were caught and arrested.

The Department of Home Affairs has confirmed that around 100 Australians who fought for or supports "Islamic extremist groups" remain in Syria and Iraq but could not confirm how many are living, dead or captured.

"The government doesn't provide a running commentary on the status of individuals in the conflict zone for security reasons," a spokesperson told News Corp Australia on Monday.

"The Australian government's capacity to confirm reports of deaths in either Syria or Iraq is extremely limited."

It came as the Syrian Democratic Forces (SDF), which is supported by the United States, prepares to seize the final 700 square km of territory held by IS in Syria including the town of Baghouz.

Greg Barton, a terrorism expert at Australia's Deakin University, said it was unlikely that many Australians remained in Baghouz.

"Clearly a lot of IS figures in northern Iraq and presumably a lot in Syria were not in this last stand and (there's) an unknown number in Turkey that may be many thousands," he said.

"So as to where the Australians are, my guess would be that quite a few are in Turkey.

"I don't think many of them will end up in this last siege. I think they would have gotten out in some of the negotiated evacuations of Raqqa and smaller settlements further east, or in other movements."