Australian counterterrorism authorities raided five properties outside of Sydney and arrested 4 men in connection with a terrorist plot to bring down an airplane.

The foiled plot was a significant departure from previous counterterrorism arrests in Australia, all of which involved low tech, "lone wolf" attacks. 

Sydney Morning Herald:

In a significant departure from the low-tech lone actor attacks that Islamic State has inspired in Australia, the group of mostly middle-aged men were allegedly working on an "elaborate" plot to build an improvised explosive device that could take down a plane.

Bomb squad officers were among dozens of police who raided five properties across Sydney on Saturday evening, smashing their way through glass doors and brick walls and arresting four men. 

Fairfax Media understands a homemade bomb was allegedly found in a Surry Hills terrace, possibly to be planted on a commercial flight to the Middle East.

The operation has forced authorities to implement emergency security arrangements at all major Australian airports.

In Sydney, enhanced security was enacted on Thursday when police received an indication of a possible threat.

The measures, including extra screening and additional checks of cabin and checked baggage, are expected to lead to longer queues and check-in times at Sydney, Melbourne, Brisbane, Darwin, Perth, Adelaide, Canberra, Cairns, Gold Coast and Hobart airports.

"We have taken this threat very seriously," Australian Federal Police Commissioner Andrew Colvin said on Sunday. "You should infer we think this was credible and there was an intention and quite possibly a capability as well." 

Khaled Merhi, Abdul Merhi, Khaled Khayat and Mahmoud Khayat were arrested at a terrace in Surry Hills and units in Renown Avenue and Victoria Road, Punchbowl, and Sproule Street, Lakemba, respectively.

They have family links to each other and links to previous plots and established networks.

Investigators believe that, based on the degree of sophistication of the plot, the group may have had some overseas direction.

Police successfully applied in court on Sunday to extend their interrogation for 24 hours.

There are few terrorist groups capable of "overseas direction" and that includes ISIS. This should come as no surprise to Australian authorities as ISIS presence has been growing in Asia and the Pacific for the last year. Several attacks have taken place in the Philippines and Indonesia in recent months and Australian authorities fear that some of the more than 100 Islamists who fought for ISIS in the Middle East could return to wreak havoc.

The men arrested yesterday were known to authorities. Unlike the French and some other countries, the Australian government appears to have kept close tabs on them, moving in after receiving intel that a plot was imminent.

It's understood an operation was being planned last week but police were forced to bring it forward drastically following information from an overseas agency.

"[We] agreed last night was the right time to go," NSW Police Commissioner Mick Fuller said. "The reality with terrorism is that you can't wait. You can't wait till you put the whole puzzle together... In this case, we risk assess regularly, hourly sometimes, around the clock."

From the way authorities are describing the plot, we can expect more arrests - possibly airport employees and certainly other confederates who assisted in getting bomb parts and finance. This was no fly by night operation. And others in the neighborhood may be implicated.

Neighbours at three of the five homes said they had seen men in religious robes coming and going in recent weeks.

A Surry Hills resident, Debbie, said she saw a group of men loitering in the street at 6am recently. They came out of Redfern Mosque and walked into the Cleveland Street home that was raided.

On Sproule Street, a resident said he had often see people in religious gear coming and going from the unit. One night recently he saw about 10 men arrive at the unit.

A wake up call for the Australian government and people. They have a far more serious Islamist problem than they previously thought.