Resolute: Premier Mike Baird, NSW Police Commissioner Andrew Scipione and Police Minister Stuart Ayres addressing the media. Credit:Jessica Hromas Allegedly coordinated to take place in Sydney and Brisbane, the executions would be spectacular, shocking, random and barbaric. The instruction allegedly came from Mohammad Ali Baryalei, the most senior Australian with Islamic State, the terrorist group also known as IS or ISIL, on Tuesday. He told his devotee in Sydney, Omarjan Azari, that it was time "show we can kill a kafir [non-believer]", according to a counter-terrorism source. Arguably the most important directive was to come later during several phone calls that stretched into the evening on Tuesday. Police will allege he ordered that Azari film the terrorist act and send it to Al Hayat Media for distribution around the world via social and mainstream media.

Fifteen people have been detained and one person charged with terrorism offences after the execution of search warrants across Sydney's north-west suburbs. Credit:NSW Police The highly sophisticated media outlet of IS, Al Hayat is infamous for its never-ending stream of propaganda videos, filmed in high definition and expertly edited with music, action scenes from the battlefield and even scenes from video games like Call of Duty. Al Hayat produced the videos of three American and British men who have all died at the hand of a fanatic's knife in the past month, appalling and transfixing the world and going a long way to spurring western military intervention. Deeply disturbing for Australians is that it appears beheadings, reserved until now for the benighted battlefields of Syria and Iraq, were to be unleashed on the streets of its major cities. With the terrorist threat level lifted to high, Australian pilots and soldiers en route to the Middle East to await the final go-ahead to "degrade and destroy" Islamic State, how severe is the threat of terrorist attacks in Australia? What can be done to defeat it?

Bonded by their fanatical support for holy war and Islamic State's self-proclaimed caliphate, the group of more than a dozen men that police alleged formed a terrorist cell first came together last year year to funnel fighters and funds to jihadist groups in Syria. Mohammad Ali Baryalei was the contact in the Middle East, shuttling between Turkey and Syria and rising through the ranks of Islamic State. A 33-year-old from a privileged Afghan family who came to Australia as a refugee, Baryalei worked as a Kings Cross bouncer and bit-part actor before being swayed to fundamentalist Islam and becoming a minor celebrity in radical circles for his "Street Dawah", videotaped kerbside conversions of Australians to Islam. In Australia, police allege that Hamdi al-Qudsi was the main operator, recruiting young men, some of them teenagers, to travel to Syria. The network supplied some 30 Australians to Syria and Iraq, around half the number of Australians who are believed to have travelled to fight in the region.

As far back as May, the intent of a group of men in Sydney and Brisbane to commit some kind of terrorist act became an active concern. Under close surveillance, counter-terrorism authorities heard of discussions about packing a car with explosives, plans that never seriously developed and were quickly abandoned in favour of something much easier to organise. As Azari - an apprentice motor mechanic from Guildford - faced court, charged with planning a terrorist attack, he was described Crown prosecutor Michael Allnut as possessing an "unusual level of fanaticism". The plot was hatched with rapid speed and done in the "full knowledge of police surveillance", Allnut said. "There was almost an irrational determination to commit that plan ... to randomly select a person to rather gruesomely execute."

An attack, police judged, was "very imminent". More than 800 police were scrambled to launch pre-dawn raids across Sydney and Brisbane, searching 25 homes in two states, detaining and questioning 15 men and charging two, including Azari, for terrorism offences. A sword was seized in Marsfield in Sydney's north-west; machetes, balaclavas, a gun and ammunition in Brisbane. . What exactly motivated the quick-fire call for terror remains unclear, although the conversation came just days after Australia announced its commitment to send 600 military personnel and military aircraft to the Middle East to prepare to wage war on Islamic State. Asked whether there was a connection, NSW Police commissioner Andrew Scipione said: "Let me answer your question by saying this - in our risk assessments, in putting together our response plan, we have certainly factored that in." Certainly, the alleged plot in Australia is only the second in a western country known to have links to Islamic State. A former IS fighter and jailer murdered four people at a Jewish Museum in Brussels in May after opening fire with an automatic weapon.

The killing of off-duty British soldier Lee Rigby in a Woolwich street by two knife-wielding Al Qaeda sympathisers approximates. But that was a brutal knife attack, rather than a beheading. What was allegedly planned for Sydney and Brisbane was far more sinister. Terrorism analysts say a beheading, especially when coupled with the drama of hostage taking, can be more powerful in terms of its psychological impacts than a mass casualty attack. "Terrorism is a form of propaganda by the deed. And the more chilling the deed, the more impactful the propaganda," Shashank Joshi, a senior research fellow of the Royal United Services Institute, wrote this week. "The graphic nature of beheading, the focus on the individual and the act of bodily desecration involved all render this far more chilling than the explosion of a bomb, even where the latter's death toll is greater."

If, as Brian Jenkins, a doyen of counter terrorism studies observed, terrorists want a lot of people watching, not necessarily a lot of people dead, a beheading is perhaps the ultimate form of sowing maximum fear with minimal resources. Jessica Stern, a veteran terrorist analyst who lectures at Harvard University, told Fairfax Media that, while relatively few are directly affected by a beheading, the psychological impact is huge. It serves multiple purposes - to instill fear, make a political point, attract recruits and provoke an over-reaction from an adversary. "They are really trying to get us to over-react. It really does seem that they are trying to get us to invade [Iraq and Syria]." On that front, Islamic State would appear to be succeeding and there are concerns that the West's armed intervention will see the terrorist group switch focus from its preoccupation with the "near enemy" to the one further afield.

The near enemy is the "apostate" Shia Muslims and other religious minorities IS has sought to purge as it advances across Iraq. The far enemy is the West. Counterterrorism authorities are worried this week's plot is not the only terrorist act being conceived by Islamic State supporters in Australia. "Chatter" picked up by intelligence agencies has prompted heightened security around parliament house and other government installations. Stern says any rise in the terrorist threat here, perhaps inevitable due military campaign against IS, should not necessarily preclude an armed response. IS has grown at an astonishing rate, and is different from other terrorist groups in that it controls large swathes of land and two large cities - Mosul in Iraq and Raqaa in Syria, she notes. Without taking action that involved deadly force, it would likely become more potent anyway.

"They have been more successful than al Qaeda," says Stern. John Horgan, a psychologist from the University of Massachusetts who has studied terrorism for 20 years says IS "truly is something different". Its gains in Iraq and Syria are demonstrable signs of its success to Islamists. "It holds very, very broad appeal," he told New York Magazine this week. "In the eyes of potential recruits, this is fantasy made reality. It's everything a would-be jihadist could have hoped for." Australia's counter-terrorism agencies are claiming a major success, as is the government. Court proceedings will determine the strength of their intelligence.

The number of police deployed on Thursday was the biggest on record, although the plot was hardly the most serious encountered in Australia over the past decade, which included more advanced plots to set off bombs at public events and launch a massacre at Holsworthy Army barracks. Nonetheless, the allegation of a discarded plan to set off a car bomb highlights the difficulties obtaining raw materials after more than a decade of strong anti-terrorism measures, including closer regulation of fertilisers and other bomb making materials and improved on-the-ground intelligence. Disrupting terrorist cells, surveillance and other intelligence gathering intelligence, as well as shutting down sources of finance, will remain integral parts of the effort to defeat IS. Military action, too, can be effective in routing IS from its safe haven, although only if it is undertaken with a broad and deep coalition that includes Muslim countries. Allied to that coalition has to be a political solution to the long-standing disputes and religious hostility in the region that feeds Islamic State. To slow the flow of recruits to IS from the West, Dr Horgan suggests a narrative needs to be articulated based on disaffected former members of IS.

"People become disillusioned if they feel that the [terrorist] group has gone too far, if they don't seem to have a strategy beyond indiscriminate killing," he says. "It's only a matter of time before those accounts leak out [of Islamic State]… We would do very well to be on the lookout." The prime minister on Friday was urging Australians to press on with their lives. "The best response to all of this is to go about one's business normally, because terrorism is about scaring people out of their ordinary daily way of life. "Second point I make is that the Government will do whatever we humanly can to keep our community safe.

"[The] third point – very important point – is that the actions yesterday were not about any particular religious group or any particular community. They were about crime, they were about potential terrorism, and they're about keeping our whole community safe." The Qur'an, like the Bible, depicts beheadings from Biblical times. Members of Islamic State undoubtedly play on the references as they adopt the practice as a terrorist tactic and recruitment tool. However, Islam's holy book also forbids the mistreatment of prisoners, orders followers of Allah not to initiate hostilities and always be inclined towards peace. Islamic State perverts and traduces the faith, and there was no better illustration than the men alleged to have planned the execution of innocents in Sydney and Brisbane. According to the police, El Baryalei spoke to Azari about wrapping the bloodied body of their victims in Islam's flag.

The shedding of any blood on the ancient black banner proclaiming the pre-eminence of Allah and the Prophet Muhammed - co-opted by IS and other jihadists groups - is strictly forbidden and widely considered a desecration by Muslims. So, too, is murdering civilians.