Jihadists returning from fighting alongside terrorists overseas are committed to trying to strike on home soil and Attorney-General George Brandis says its ''delusional'' to think otherwise.

Senator Brandis wants to boost the powers of spy agencies to deal with what he says is the growing threat of "home-grown terrorism".

Attorney-General George Brandis Credit:Andrew Meares

"Anyone who thinks there aren't people in the West, including in Australia, who are committed to this course of action I'm afraid is delusional," Senator Brandis told ABC News Radio.

"It's a really insidious threat which often cannot be properly dealt with without the collection of intelligence, I'm afraid that's the reality of the world in which we live," he said.