The defeat of the Islamic State caliphate in Syria is “imminent” according to the Australian Defence Force, raising fresh questions over how to deal with up to 100 Australians who fled to fight with the terrorists.

The drama is already playing out in Britain, where IS schoolgirl Shamima Begum, 19, recently surfaced in a refugee camp begging to return home with her new baby, the only surviving child after her two other babies perished.

One of the friends of the British schoolgirl, Amira Abase, married Australian teenager Abdullah Elmir, who was dubbed the “Ginger Jihadi”.

Britain moved swiftly to instead cancel Begum’s citizenship, despite her lawyers insisting it would render her stateless.

This is the moment @RohitKachrooITV handed Shamima Begum the letter from the Home Office confirming she's been stripped her of UK citizenship.

She said the decision was "kind of heart-breaking to read" and "hard to swallow" https://t.co/atNmGGkvpi pic.twitter.com/jvZAxjywag

— ITV News (@itvnews) February 20, 2019

An estimated 100 Australians are believed to be still alive after fleeing to fight for IS, including women who married IS fighters overseas and had babies that may have a right to claim Australian citizenship by descent. More than 240 passports have been cancelled to stop fighters fleeing overseas.

Acting chief of the Australian Defence Force Vice Admiral David Johnston told Senate estimates that while the defeat of the physical, land-based caliphate is imminent, the fight will continue.

“The land-based caliphate element of DAESH is likely to be defeated within the next few weeks,” he said.

“The caliphate defeat is imminent – the physical caliphate.

“The judgement that we are seeing is that within days or weeks that remaining small pocket of quite hard-core fighters in that area are likely to be defeated by the SDF forces on the ground.”

Acting Defence Force chief Vice Admiral David Johnston at Senate estimates in Canberra on Wednesday. Photo: AAP

Labor’s Penny Wong asked whether the Australian government agreed with the assessment that a US military presence was no longer required on the ground in Syria.

“You would be aware DAESH have collapsed down to the south-eastern part of Syria, in what’s called the middle of the Euphrates River valley,” Vice Admiral Johnston said.

“The assessed area that the fighters of DAESH hold is about a 700-square-metre area at the moment.”

Men walk amid debris in the Islamic State’s former Syrian capital of Raqa on Tuesday. Photo: AFP/Getty

Last year, The Australian newspaper reported that one jihadi bride and her child had quietly returned to Australia.

On Monday, ASIO director-general Duncan Lewis told a Senate estimates that many of the Australian fighters had already fled to other areas of the Middle East.

“ISIL’s military losses in Syria and Iraq – while great – will not eliminate the threat it poses to this country and to our interests,” Mr Lewis said, using an acronym that stands for Islamic State of Iraq and the Levant.

“We expect the threat from ISIL-inspired lone actors will endure.”

He predicted that many would attempt to disappear into the Middle East rather than return home to Australia.

“It is likely some ISIL fighters and their families have tried to ­depart Syria, and thousands have been detained in Syria and Iraq,” he said.

“Others may travel to alternative conflict zones, but this will ­depend on each individual’s contacts, language skills, cultural ­affinity and associated networks.”

Among the IS sympathisers being held by US-backed fighters is the US-born wife of an Australian Islamic State fighter, Hoda Muthana who married Suhan Abdul Rahman.

"I hope America doesn't think I'm a threat to them and I hope they can accept me."

24-year-old American Hoda Muthana describes to @jamesaalongman her decision to join ISIS in Syria and whether she expects punishment if she is able to return to the U.S. https://t.co/zVlEhFp070 pic.twitter.com/Oz5EXrYOiy

— ABC News (@ABC) February 20, 2019

On Wednesday, the Morrison government introduced the Counter-Terrorism Legislation Amendment Bill, which will introduce the presumption against bail and parole for people who have demonstrated support for, or have links to, terrorist activity.

“This Bill will help protect the community from dangerous individuals like Yacqub Khayre, who committed an appalling terrorist attack in Brighton, Victoria in 2017,” Attorney-General Christian Porter said.

“Mr Khayre was on parole for state crimes committed in Victoria and had previously been charged with terrorism offences.”

The new laws will also strengthen the high-risk terrorist offenders (HRTO) scheme to ensure that terrorist offenders who are serving multiple sentences stay in jail.

“There are currently 38 terrorist prisoners eligible for continuing detention under the HRTO scheme. Nine of these individuals are due for release over the course of the next two years,” Home Affairs Minister Peter Dutton said.

“The Morrison government is determined to ensure that dangerous terrorist offenders stay in prison.”