The growing number of young people caught up in terrorism is worrying Australia's primary national security agency.

The Australian Security Intelligence Organisation identified people under the age of 18 involved in violent extremism and warned that minors had not only conducted terrorist attacks, but held leadership positions in terrorist groups.

"Violent extremist narratives ... particularly appeal to teenagers, and may resonate with some minors' feelings of alienation, unease about the future and mistrust of adults," it says in its annual report released on Tuesday.

Australia's terrorism threat remains at probable, meaning there is intelligence to suggest people in the country have the motivation and ability to carry out an attack.

Future terrorist attacks in Australia are likely to be undertaken by lone wolves using simple weapons to target public spaces, making them harder for security agencies to detect.

There were two terrorist attacks by lone actors who used simple weapons in 2020/21 and three major attacks were prevented in the past year.

ASIO says this kind of attack is difficult to detect as it can arise with little forewarning.

But espionage and foreign interference are expected to leapfrog terrorism as Australia's primary security concern over the next five years.

ASIO director-general Mike Burgess said the number of attack attempts from foreign spies was "unacceptably high".

"These attempts occur on a daily basis," he said.

Foreign actors are also monitoring, coercing and threatening people from certain cultural communities within Australia but no county was named in the annual report.

The national security organisation disrupted a "nest of spies" in 2020, where the group developed relationships with current and former politicians and with people who had access to sensitive information.

The group was removed from Australia.

Mr Burgess also expressed concern about Australian cyber infrastructure, particularly in the areas of telecommunication and energy, being sabotaged.

Australian Federal Police charged 25 people with terrorism offences and were part of more than 400 terrorism "disruptions" across 22 countries in the past financial year.

Twenty-four convicted terrorists will become eligible for release over the next decade.

Australian Associated Press