Counterterrorism raids in Sydney on Thursday were sparked by security intelligence that the Islamic State in Iraq and the Levant terrorist group was planning a random, violent attack in Australia

Counterterrorism raids in Sydney on Thursday were sparked by security intelligence that the Islamic State in Iraq and the Levant terrorist group was planning a random, violent attack in Australia as a demonstration of its reach, the prime minister said.

Australian police detained 15 people and raided more than a dozen properties across Sydney in the country's largest counterterrorism operation, saying intelligence indicated an attack was being planned on Australian soil, according to the Associated Press.

Prime Minister Tony Abbott said he had been briefed on Wednesday night about the operation that was prompted by information that an ISIL leader in the Middle East was calling on Australian supporters to kill.

Abbott was asked about reports that the people detained were planning to publicly 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."

"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 added.

Abbott did not name the Australian.

About 800 federal and state police officers were involved in the Sydney operation — the largest in Australian history, Federal Police Deputy Commissioner Andrew Colvin said. Police also conducted raids in the eastern cities of Brisbane and Logan.