A federal parliamentary committee has been told a terrorist attack is anticipated in Australia in the next 12 months.
ASIO boss Mike Burgess told an inquiry in Canberra on Thursday that Sunni-based violent extremism remained the major concern of security agencies, based on the current caseload.
Mr Burgess told the Parliamentary Joint Committee on Intelligence and Security:
"However, given the growth that we've seen in nationalist and violent extremism, we anticipate there will be a terrorist attack in this country in the next 12 months and it can come from either ideology.
"For me, it doesn't really matter because they are both capable of actually conducting acts of violence and that's where we focus."
Mr Burgess said racist supremacist groups had risen from one-third of the agency's caseload to 40 per cent.
"This is a growing problem for this country," he said.
Sunni-based violence remained the greatest threat, mostly city-based, and battle-hardened foreign fighters are still seeking to return to Australia, he said.
But ASIO was also facing a "growing assortment of ideologically violent extremists", he said.
"We need to know why people are driven to these views."
For ASIO, the national terrorism threat level remains probable as it has credible intelligence that individuals and groups have the will and capability to conduct an attack in Australia.
Terrorist propaganda continues to resonate with extremists in Australia, and such messaging is drawing a younger audience.
Australians as young as 13 and 14 are involved in Islamic extremist and extreme right-wing circles, according to the national surveillance organisation's written submission.
-- with AAP