"Young Australians, some of them children, have been brainwashed online, sometimes under the very noses of their parents," he said.
"Too many times, young Australians end up at the other end of the world, committing crimes and horrific acts of violence."
But he had a warning: "If you survive and seek to return, expect to face the consequences. You will face the full force of the law. This government will do everything in our power to protect our people and to stop radicalised and brutalised people from roaming our streets."