Federal Justice Minister Michael Keenan says it is impossible to say there will never be another terrorist attack in Australia, even as the nation ramps up its efforts to combat extremists.

Mr Keenan said six attempted terrorist incidents have been stopped by security agencies since two successful attacks – the Lindt cafe siege in December, and the stabbing attack on police by a Melbourne man last September.

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“So the scale of the threat is enormous and no person could realistically stand before you and say that there is no chance of another successful terrorist attack in this country,” he he told a Lowy Institute function in Sydney on Friday.

“But I can say that the government, with our partners in the states and territories, are doing absolutely everything we can to stop that happening.”

Mr Keenan warned that in the fight against home-grown terror attacks, parents had to monitor their children’s use of social media and the internet.

He said Islamic State, also known as ISIL, had a sophisticated online propaganda program targeting young people who are vulnerable to radicalisation.

“Research has found that ISIL supporters have three times more global friends on Instagram compared to the average Australian user,” he said.

“On Twitter the Brookings Institute found that ISIL and its supporters had at least 46,000 active accounts, each with an average of 1,000 followers.

“This indicates that they have developed a deep and pervasive network of supporters that can spread their messages instantaneously across all corners of the globe.”

Mr Keenan said he would visit Malaysia, Indonesia and Singapore in August to discuss improved cooperation on combating terrorism and radicalisation.

– AAP