ISIS is back and the terror group is actually “expanding and building its strength” around the world, an expert has warned.

The extremist sect was believed to be on its knees when its stronghold in Raqqa was liberated in October last year.

But last week's knife rampage in Melbourne has served as a reminder that the threat is still real.

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Professor of global Islamic politics Greg Barton at Australia's Deakin University has warned the world not to be complacent.

“We lulled ourselves into a false sense of security,” he told news.com.au.

“They are not controlling a caliphate now but unfortunately they are still a very potent force.”

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