Fears of extremists carrying out "demonstration killings" led to the country's largest ever anti-terror raids by police, Australia's Prime Minister has said.
More than 800 officers took part in the operation which saw at least 15 people detained and one charged with a serious "terrorism-related" offence.
Police said intelligence indicated a random, violent attack was being planned.
The early morning raids of homes and businesses in Sydney and Brisbane came just days after Australia raised its national terror threat level to "high" for the first time, citing the likelihood of terrorist attacks by Australians radicalised in Iraq or Syria.
Tony Abbott told reporters the operation had been prompted by information that an Australian, who is senior in the Islamic State militant group, had been calling on supporters in Australia to "conduct demonstration killings".
He said: "Quite direct exhortations were coming from an Australian who is apparently quite senior in ISIL to networks of support back in Australia to conduct demonstration killings here in this country.
"This is not just suspicion, this is intent and that's why the police and security agencies decided to act in the way they have."
He did not name the Australian.
Andrew Scipione is the New South Wales Police Commissioner:
