CANBERRA, Australia -- The Islamic State plot to carry out random beheadings in Sydney alleged by police is a simple and barbaric scheme that has shaken Australians. But terrorism experts on Friday questioned whether the ruthless movement had the capacity or inclination to sustain a terror campaign so far from the Middle East.
Police said they thwarted such a plot by detaining suspects and raiding more than a dozen properties across Sydney on Thursday.
The Islamic State militant group has beheaded three Westerners in the Middle East in recent weeks and recorded the brutal slayings to make propaganda videos widely condemned.
Two of the 15 people whom police had detained Thursday have been charged. Nine were freed before the day was over, and the rest released on Friday.
Prime Minister Tony Abbott conceded it was difficult to safeguard the Australian population against such attacks.
"The regrettable reality is that to mount the kind of attacks which ISIL in Syria and in Iraq has in mind for Australia, all you need is a determined individual who will kill without compunction, a knife, an iPhone and a victim," Abbott told Seven Network television on Friday, using one of Islamic State's former names, Islamic State of Iraq and the Levant.
Some terrorism experts saw the plot as a potential shift in Islamic State's focus from creating an Islamic caliphate in the Middle East. Others said it is more likely a symptom of policy confusion within a disparate group.
"If you have people coming in from different backgrounds from all these countries, when it comes to policy making, they're going to fight each other, they're going to kill each other," said Samuel Makinda, professor of International Relations and Security Studies at Murdoch University.
"On ISIS, I see no direct threat to Australia or to any other country at the moment except those in the Middle East," he added, using the movement's former name, Islamic State of Iraq and Syria.
The raids involving 800 federal and state police officers came in response to intelligence that an Islamic State group leader in Syria was calling on Australian supporters to kill, Abbott said.
Hundreds of Muslims in the Sydney suburb of Lakemba protested the raids on Thursday night, with speakers accusing the government of exploiting public fear in a bid to get contentious counterterrorism laws through Parliament.
Abbott defended the raids against accusations of overkill.
"It was a show of strength," Abbott told reporters. "It needed to be a show of strength. It needed to be a demonstration that we will respond with strength to any threat to our way of life and to our national security."
Abbott said armed police were taking over security at Parliament House in Canberra, because Australian Islamic State fighters in Iraq and Syria had been urging their supporters at home to attack the building and government members.
With national grand finals approaching in Rugby League and Australian Rules Football -- among the country's most popular sports -- police have said security will be boosted at sports arenas and other public venues attracting large numbers of people.
Greg Barton, a Monash University global terrorism expert, said Islamic State could be starting to direct its global followers to take the fight to their home communities in a bid to usurp al Qaeda's position as the leading global jihadist network.
The movement could eventually mount attacks in Australia like last year's massacre by militant group al-Shabaab on the Westgate Mall in Nairobi, Kenya, that killed 67, Barton said.
It might also become capable of replicating in Australia the London public transport bombings of 2005 which killed four suicide bombers and 52 victims.
"We don't think they have that capacity right now ... so our more immediate threats are things like the Woolwich killing which are very low tech," said Barton, referring to last year's slaying in the London suburb of Woolwich. Two extremists ran a soldier down in a car then stabbed and hacked him to death in public.
"Its power of persuasion at the moment is considerable," Barton said of Islamic State. "Whether it's got many followers here in Australia who have much technical nous is not clear."
The government estimates Islamic State has 100 supporters within Australia.
Security authorities are particularly concerned by the dozens of Australian jihadists who have already returned home after fighting for Islamic State or another al Qaeda offshoot Jabhat al-Nursa, also known as the Nusra Front, in Iraq and Syria. Their combat and bomb-making training could make them potent terrorists.
But Clive Williams, a counterterrorism expert at the Australian National University and a former military intelligence officer, said Islamic State supporters who can't join the fight because their passports have been cancelled on security grounds are more worrying.
"The ones who are coming back aren't a problem because maybe they're less committed, or maybe they're less enchanted," Williams said. "The ones who come back are less of a problem than the ones who want to go."
Thursday's raids came just days after Australia raised its terrorism threat to the second-highest level in response to the domestic threat posed by Islamic State supporters.
Federal Police Acting Commissioner Andrew Colvin said police conducted additional raids in Sydney Thursday night. No one was arrested as a result of those raids.
One of those detained, 22-year-old Omarjan Azari of Sydney, appeared in court on Thursday charged with conspiracy to prepare for a terrorist attack. Another man faces a lesser weapons charge.
Mohammad Ali Baryalei, believed to be Australia's most senior Islamic State member, was named as a co-conspirator in court documents. Police have issued an arrest warrant for him.
Associated Press writer Kristen Gelineau in Sydney contributed to this report.
