By Kirsty Needham

SYDNEY, Dec 6 (Reuters) - One in five priority counter-terrorism cases investigated by Australia involved youth, the country's spy chief said on Friday, as the "Five Eyes" intelligence partners warned about the radicalisation of young "digital natives".

Mental health, education and social services needed to intervene in many cases before the behaviour of minors became a police issue, said a research paper by the Five Eyes, which also include the U.S., Canada, Britain and New Zealand.

"Around 20% of ASIO's priority counter-terrorism cases involve young people. In every one of the terrorist attacks, disruptions and suspected terrorist incidents in Australia this year, the alleged perpetrator was a young person," Australian Security Intelligence Organisation (ASIO) Director-General Mike Burgess said in a statement.

"As a parent, the numbers are shocking. As an intelligence officer, the numbers are sobering," he said.

The Australian Federal Police $(AFP.UK)$ had investigated 35 teenagers aged 17 years or younger, including a 12-year-old, in terrorism investigations since 2020, said AFP Commissioner Reece Kershaw.

Over half of them were charged with offences, he said.

In one Australian case described in the report, a 16-year-old involved in a local and international network shared violent extremist material calling for attacks on non-Caucasian people, and "urged others to prepare for an upcoming race war to 'defend the white race'".

The teenager had few real-world relationships and spent little time socialising offline, it said. He was arrested and sentenced to 18 months jail.

In another Australian case, a 14-year-old with nationalist and racist extremist views used a Snapchat account to plan a violent attack, and after being arrested by police undertook programmes on countering violent extremism.

"We are witnessing the same extremist propaganda videos across multiple unrelated investigations, and this suggests that links exist in the online environment across platforms such as Discord, Telegram and TikTok," said Kershaw.

Australia passed legislation this month to ban children under the age of 16 years from social media platforms starting late next year.

(Reporting by Kirsty Needham; Editing by Sonali Paul)

((Kirsty.Needham@thomsonreuters.com;))