Militants connected with radical group Islamic State (also known as Isis or Isil) were planning to behead a member of the public in Australia, Prime Minister Tony Abbott said yesterday, after hundreds of police raided homes in a sweeping counter-terrorism operation.

Abbott said there was a “serious risk from a terrorist attack” days after Australia raised its national terror threat level to “high” for the first time, citing the likelihood of attacks by Australians radicalised in Iraq or Syria.

Australia is concerned over the number of its citizens believed to be fighting overseas with militant groups, including a suicide bomber who killed three people in Baghdad in July and two men shown in images on social media holding the severed heads of Syrian soldiers.

Militants were planning to behead a member of the public

More than 800 police were involved in the pre-dawn security operation in Sydney and Brisbane, which was described as the largest in Australian history and resulted in the detention of 15 people, police said. Abbott told a news conference that members of the radical group had planned to conduct a public beheading. “That’s the intelligence we received,” he said.

Media reported that the plans included snatching a person at random in Sydney, Australia’s largest city, and executing them on camera draped in the group’s black flag.

“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,” Abbott said, referring to the group otherwise known as Islamic State that has seized large swaths of territory in Syria and Iraq.

Sydney man Omarjan Azari, 22, appeared in court after the raids. He has been charged with conspiracy to commit a terrorist act and will remain in custody until a hearing in November, authorities said.

Prosecutor Michael Allnutt told the court in Sydney that an attack was being planned that “was clearly designed to shock and horrify, perhaps terrify” the community, the Sydney Morning Herald reported.

Azari’s lawyer, Steven Boland, did not apply for bail. Boland told the court the allegation was based on one phone call, according to media reports. Boland was not available for comment.

Police said the raids were focused in western Sydney and the Queensland state capital of Brisbane, where two men were arrested on terrorism-related charges last week.

About half of Australia’s population of roughly 500,000 Muslims lives in Sydney, with the majority in the western suburbs where the raids occurred.

New South Wales Police Commissioner Andrew Scipione said he had ordered more police onto the streets after the raids to prevent “troublemakers” taking advantage of the tension.

However, in western Sydney’s Lakemba neighbourhood, which is home to one of the country’s largest Muslim populations, there was little sign yesterday of any increased security presence.

Several residents interviewed by Reuters said they had not heard about the raids and expressed disbelief about the plot.

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