More than 800 Australian law enforcement officials descended on more than a dozen homes and arrested ISIS members planning a the beheading of a random citizen and the assassination of Prime Minister Tony Abbott, according to the Associated Press.

They also report that 9 of the 15 suspects arrested were released before the end of the day.

Police on Thursday said they thwarted a plot to carry out beheadings in Australia by supporters of the radical Islamic State group. They detained 15 people and raided more than a dozen properties across Sydney, though nine of those brought in were freed before the day was over.

The raids involving 800 federal and state police officers - the largest in the country's history - came in response to intelligence that an Islamic State group leader in the Middle East was calling on Australian supporters to kill, Prime Minister Tony Abbott said.

Abbott was asked about reports that the detainees were planning to behead a random person in Sydney.

"That's the intelligence we received," he told reporters. "The exhortations - 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."

ISIL refers to the al-Qaida splinter group leading Sunni militants in Iraq, Islamic State of Iraq and the Levant, which now calls itself simply Islamic State.

"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," Abbott said.

Nine of those detained were later released, New South Wales police said. They did not say why, or whether they will face charges later.

The raids came just days after the country raised its terrorism threat to the second-highest level in response to the domestic threat posed by supporters of the Islamic State group. At the time, Abbott stressed that there was no information suggesting a terror attack was imminent.

Later Thursday, Attorney General George Brandis confirmed that a person born in Afghanistan who had spent time in Australia and is now working with the Islamic State group in the Middle East ordered supporters in Australia to behead people and videotape the killings.

"If the ... police had not acted today, there is a likelihood that this would have happened," Brandis told the Australian Broadcasting Corp.

ISIS has made the existential leap from organization to ideology. This is incredibly dangerous because it means that no matter how successful we are in destroying them in the Middle East, random attacks and lone wolf jihadists will still threaten us.

As we've seen in the past, counter terrorism is part luck, and part superior police work. The Aussies appeared to get lucky in intercepting a call and then carried out a textbook raid to sweep up the suspects. Congratulations to the Australian security forces for their display of competence and excellent coordination.