The Australian police arrested 15 people Thursday in a major counter- terrorism operation. They also charged one person with serious terrorism-related offenses.

The operations were triggered by an intelligence report that Islamic State militants were planning to conduct a demonstration killing in Australia, Prime Minister Tony Abbott 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," Abbott said.

"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, reports the Associated Press.

About 800 law enforcement officials conducted raids on many properties across Sydney as a part of the operation, Australian Federal Police Deputy Commissioner Andrew Colvin said. Raids were also carried out in the cities of Brisbane and Logan.

The police have issued an arrest warrant for a Mohammad Ali Baryalei, 33, a former Sydney night club bouncer. Baryalei is suspected to be Australia's senior most member of the Islamic State.

One of the men arrested was 22-year-old Omarjan Azari. He was charged with conspiracy to perpetuate a terrorist attack.

According to court documents, Azari was accused of plotting with Baryalie and other militants of planning a terrorist attack, reports AP.

The arrests come in the backdrop of the Australia raising its terror threat level to high last week.

Meanwhile, Opposition Leader Bill Shorten said that the allegations were really horrifying.

"These raids will no doubt come as a shock to many Australians, it's a development that reminds us all how close to home the threat of terrorism can be," he said., reports The Sydney Morning Herald.

Immigration Minister Scott Morrison said that the range of the police operation shows the gravity of the threat Australia faces. He also said that the government had taken a bold stand in dealing with the threat both inside and outside the country.