MELBOURNE (AFP) - At least 12 Australian women from one city have attempted to join the Islamic State in Iraq and Syria (ISIS) group, police said on Friday, warning of a trend towards a "romanticised view" of violent Islamists.

More than 100 Australians have left the country to support ISIS in Syria and Iraq, raising concerns about radicalisation and whether they pose a security threat on return, the authorities have said. At least 30 have been killed overseas.

Victoria Police assistant commissioner Tracy Linford said those attracted to ISIS were mostly young, isolated people swayed by slick social media propaganda.

In the case of women, they often had a romantic idea of what life would be like under ISIS control, she said, adding that at least 12 had attempted to join from Melbourne, Victoria's capital city.

"We've got five (women) that we know are over there," Linford said, adding that two more were unaccounted for, four were turned back outside Australia and one was stopped at the airport before leaving.

"But we also suspect that there are probably more than 12," she told reporters.

Linford's comments came just days after a Sydney mother reportedly abandoned her two children and fled to Syria for a new life under ISIS.

"We think that the young women particularly get a romanticised view of what actually exists for them if they travel to the conflict zones," she said.

"There is a reach-back from people who are already in the conflict zone telling them, 'Come over... you will be well looked after, you will have an important position in growing the caliphate, bearing jihadi children in the future, growing the Islamic State'.

"And I think they think they are going to be put on a pedestal and treated very well once they are overseas, but the reality is, that's not the case." Linford said some women were forced into arranged marriages and others pushed into sexual servitude, while living in often squalid conditions and on rations, with their movements heavily restricted.

"One of things we know about ISIS is that their social media skills are well advanced, and their reach through social media is obviously paying dividends for them," she said, using another acronym for the Islamists.

Earlier this week Prime Minister Tony Abbott said dual nationals linked to terrorism would be stripped of their Australian citizenship.

Australia raised its threat level to high last September and has since carried out a series of counter-terrorism raids, with several alleged plots foiled this year.