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 a plot to carry out beheadings in Australia by Islamic State group supporters when they raided more than a dozen properties across Sydney on Thursday.

Two of the 15 suspects detained by police were charged on Thursday, officials said. Nine others were freed before the day was over.

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 a name that Islamic State no longer goes by, 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 — the largest in the country’s history — came in response to intelligence that an Islamic State group leader in Syria was calling on Australian supporters to kill, Abbott said.

The raids sparked protests by hundreds of Muslims in the Sydney suburb of Lakemba on Thursday night, where speakers accused the government of exploiting public fear in a bid to get contentious counterterrorism laws through Parliament.

Abbott said Friday that police were taking over security at Parliament House in Canberra, telling Australian Broadcasting Corp. radio that the building, “government and government people” had been identified as targets.

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 stepped up at sports arenas and other public venues where people gather in large numbers.

Greg Barton, a Monash University global terrorism expert, said that Islamic State could be starting to direct its global followers to take the fight to their home communities in a bid to usurp al-Qaida’s position as the leading global jihadist network.

The movement could eventually mount attacks in Australia like the attack last year by militant group al-Shabaab gunmen on the Westgate Mall in Nairobi, Kenya, that claimed 67 lives, 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.

“More immediately, 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 the murder last year 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-Qaida 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 canceled on security grounds are more worrying.

“The conventional wisdom is we’re worried about the ones who are coming back. But in fact, 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,” he added.

Thursday’s raids came just days after the country raised its terrorism threat to the second-highest level in response to the domestic threat posed by supporters of the Islamic State group. At the time, Abbott stressed that there was no information suggesting a terror attack was imminent.

Mohammad Ali Baryalei, who is believed to be Australia’s most senior member of the Islamic State group, was named as a co-conspirator in court documents filed Thursday. Police have issued an arrest warrant for Baryalei, a 33-year-old former Sydney nightclub bouncer.

One of those detained, 22-year-old Omarjan Azari of Sydney, appeared in a Sydney court on Thursday charged with conspiracy to prepare for a terrorist attack. He faces a potential life sentence if convicted.

A second man was charged Thursday night in connection with the raids. The 24-year-old, whom police didn’t name, was charged with possessing ammunition without a license and unauthorized possession of a prohibited weapon. He was released on bail and ordered to appear in court next week.

Two women who were among those detained were issued notices to appear in court at a later date and released. They have not been charged.

–Rod McGuirk / Associated Press. Associated Press writer Kristen Gelineau in Sydney contributed to this report.