SYDNEY — Australian police thwarted an alleged Islamic State plot to abduct and behead a member of the public as officers detained 15 people in the nation’s largest- ever anti-terrorism operation.
Authorities carried out the pre-dawn raids in Sydney Thursday after receiving intelligence that a senior Islamic State member was urging supporters in Australia to carry out ‘‘demonstration killings,’’ Prime Minister Tony Abbott told reporters.
The operation, along with raids in Queensland state, came days after the government raised Australia’s terror alert to the highest level in a decade, citing the threat posed by local supporters of Islamic State. Abbott, who will host world leaders at November’s Group of 20 summit in Brisbane, has committed 600 military personnel to the U.S.-led fight against the group in the Middle East.
‘‘We are at serious risk from a terrorist attack,’’ Abbott said. ‘‘There are networks of people here in this country, who despite living here, despite enjoying the Australian way of life, they would do us harm.’’
Omarjan Azari, 22, appeared in a Sydney court Thursday charged with preparing and planning for a terrorist act and with conspiring with Mohammad Baryalei, who is overseas and wanted by Australian police for alleged terrorism-related activity.
Prosecutor Michael Allnutt said the planned act was designed to ‘‘shock, horrify’’ and terrify the public. Defense lawyer Steven Boland said the allegations were based on one intercepted phone call. Azari, who didn’t apply for bail, was remanded in custody and the case was adjourned for Nov. 13.
Australia is strengthening laws against domestic supporters of extremist groups and says at least 60 of its citizens are fighting with militant groups in Syria and Iraq.
The government has said that 20 Australians have returned from fighting with jihadists abroad and about 100 more are funding or facilitating militants. The Australian newspaper last month ran a front-page photo posted on Twitter by Australian jihadist Khaled Sharrouf, who fled to Syria last year using his brother’s passport, showing a young boy holding what’s purported to be the severed head of a dead Syrian soldier.
Federal police on Sept. 10 arrested two Brisbane men for allegedly ‘‘recruiting, facilitating and funding people to travel to Syria to engage in hostile activities.’’
A Sydney-based money transfer company was suspended from trading yesterday on suspicion it was involved in terrorism financing.
Thursday’s raids were carried out by 800 officers in 12 suburbs in northwest Sydney, Australian Federal Police Acting Commissioner Andrew Colvin told reporters.
The operation is ‘‘very much about police disrupting the potential for violence against the Australian community at the earliest possible opportunity,’’ Colvin said.
Asked to comment on reports that people were prepared to carry out public beheadings in Australia, Abbott responded: ‘‘That’s the intelligence we received.’’
‘‘Quite direct exhortations were coming from an Australian, who is appparently quite senior in ISIL, to networks of support back in Australia to conduct demonstration killings here in this country,’’ he said.
Islamic State has released videos showing the beheadings of three foreign hostages — U.S. journalists James Foley and Steven Joel Sotloff and British aid worker David Haines.
Nick O’Brien, a former special branch head of international counter-terrorism at London’s New Scotland Yard, said the fatal attack on British soldier Lee Rigby in the Woolwich neighborhood of southeast London in 2013 demonstrated the dangers posed by extremists.
‘‘All you need is someone with a machete and the intent to do it,’’ said O’Brien, who worked as a U.K. police liaison officer in Australia. ‘‘Is the threat real? Yes, absolutely.’’
New South Wales Police said officers had been tasked with preventing reprisal attacks against the Muslim community.
A quarter of Australia’s population was born overseas, with 43 percent having at least one overseas-born parent, according to the 2011 census. The number of Muslims rose 69 percent in the decade to 2011 to 476,300, or 2.2 percent of the population of 21.5 million at the time, the data show.
Abbott said at the weekend Australia will deploy 400 air force personnel and 200 special forces soldiers to a U.S. military base in the United Arab Emirates along with fighter jets, as a coalition formed by President Barack Obama prepares to step up the fight against Islamic State.
The government raised the National Terrorism Public Alert System to high from medium on Sept. 12, the second-highest level, indicating the government and intelligence authorities believe an attack is likely.
Raising the alert will mean increased security screenings at airports, ports, government buildings and public gatherings such as major sporting events.
Abbott’s Liberal-National coalition government last month committed an additional A$630 million over four years to counter-terrorism measures. It plans to introduce security laws that will allow the arrest and jailing of returning foreign fighters while preventing extremists from departing Australia.
Resentment among those who’ve been blocked by Australia from traveling to Syria or Iraq to fight may be more concerning to authorities than those returning from the region, Clive Williams, who last served as director of security intelligence within Department of Defence until 2002, said by phone.
‘‘There may be around 60 people in that category at the moment, who have had their passports denied or withdrawn,’’ Williams said. ‘‘Those ones who have come back, in the U.K experience, have not been a problem, as they’ve got the frustration out of their system and the reality of being in Syria has been somewhat different to what they had anticipated.’’
_ Stringer reported from Melbourne.