His renewed warning follows the arrest of a 29-year-old woman at Sydney Airport as she was preparing to leave Australia on an international flight.
Counter-terrorism police have charged her with supporting incursions into a foreign state with the intention of engaging in hostile activities.
She's been released on bail and will face court next month.
Western governments are warning the increasing number of foreign fighters in Syria poses a potential terrorist threat and several countries are meeting in Brussels this week to look at what additional steps they can take.
Dr Rodger Shanahan from the Lowy Institute for International Policy told Greg Dyett their options are limited.
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