A 21-year-old Sydney man who allegedly supports Islamic State progressed on a path of radicalisation that eventually led to his arrest for terrorism offences, authorities say.
The Riverwood man was arrested at home on Wednesday morning by counterterrorism police and has been charged with preparing possible terrorist acts, advocating terrorism and being a member of a terrorist organisation.
Police say the man had, over the past six months, posted increasingly extremist material online and sought to convince others - particularly teenagers aged 17 and 18 - to pledge allegiance to IS.
The accused also allegedly downloaded a document on how to use knives and other blunt instruments in a terrorist attack.
Australian Federal Police assistant commissioner Ian McCartney says the man's activity was exclusively online.
He'd not yet established a specific target and did not provide an immediate threat.
"We decided to act early because we needed to - we were concerned," Mr McCartney told reporters in Sydney.
"It's fair to say there was a continuum in terms of radicalisation and we were getting concerned that continuum was increasing ... (to) radicalisation to the point of encouraging politically-motivated violence."
Authorities say the 21-year-old was connected to others previously charged with terrorism offences in Australia.
Mr McCartney on Wednesday said authorities had relied upon 2018 cybersecurity legislation to access the man's encrypted communications.
A terror attack in the United Kingdom last week - during which two people were fatally stabbed on London Bridge - was "not a key factor" in Wednesday's arrest but prompted authorities to keep a keen eye on the accused, the assistant commissioner said
"When there's a terrorist act committed in another country that generates significant media attention we're always concerned what impact that will have on people in Australia in terms of that radicalisation continuum."
Additional arrests are not anticipated.
The man has been refused bail to appear in the Parramatta Local Court on Thursday.
"The activity today is a reminder to all Australians that this threat hasn't gone away," Home Affairs Minister Peter Dutton told reporters in Canberra.
"As we saw in London very recently, people want to do harm in a country like ours and the UK."