The brother of a Sydney man arrested over an alleged plot to bring down a plane is reportedly a senior Islamic State fighter in Syria.
Khaled Khayat, aged in his 50s, is the apparent instigator of the planned terror attack, according to ABC reports.
He was taken into police custody along with his relative Mahmoud Khayat and father-and-son pair Khaled Merhi and Abdul Merhi on Saturday after coordinated raids at their properties across Sydney.
Khaled Khayat's brother is believed to be a senior Islamic State fighter in Syria, while Khaled and Abdul Merhi are believed to be relatives of another notorious Islamic State fighter, Ahmed Merhi, a former Sydney man who travelled to Syria in 2014.
On Sunday, the AFP was granted permission by a court to hold the men for up to a week without charge under tough anti-terror legislation.
The four men allegedly hatched the bomb plot with assistance from IS in Syria, and were only discovered when international intelligence agencies intercepted communication between the men in Australia and Syria, The Sydney Morning Herald reports.
It was these international tip-offs from UK and U.S. intelligence authorities that prompted Australian authorities to conduct coordinated raids on the Sydney suburbs of Surry Hills, Punchbowl, Wiley Park and Lakemba.
According to a report in The Australian on Tuesday, the police only came down on the suspected terrorists after British authorities threatened to place travel warnings on flights to Australia -- a report which Justice Minister Michael Keenan has refused to confirm or deny.
Keenan had earlier said the terror plans were "quite a sophisticated plot" with a "horrendous objective".
None of the men have yet been charged.
A kitchen meat mincer was among the items seized by the AFP during Saturday's raids. It's believed that a noxious gas or explosives were to be set off using the mincer on board a flight.
On Monday, police officers uncovered a flight slip with the number of a route from Jakarta to Sydney while combing through the garbage bins of a raided property in Lakemba.
Neil Fergus, Chief Executive of the Intelligent Risks Group labelled the planned raids the "most significant aviation security threat that we have had in this country for many years."
This attack differs from other terror plots in Australia in recent years, which have been planned and carried out by so-called "lone wolf" attackers.
"So we have a quite sophisticated terrorist conspiracy, in contrast to several of the more low-tech, unsophisticated conspiracies which have been thwarted in Australia in recent times," he told the ABC's 7:30.
Jacinta Carroll is from the Australian Strategic Policy Institute and highlights that the group element of this conspiracy and the direct communication with Islamic State is what makes it both unique and concerning.
"These networks, whether they're familial or otherwise, are very important and of concern. And that's why Australia and other countries have been so concerned about preventing the travel of their own individuals as foreign fighters," Carroll told 7.30.
"There is an organised cell that has a level of technical capability and access to materials that authorities have assessed poses a credible risk and, unusually... this is one that was seeking to attack a very hard target."
Following the arrests and raids, security across all Australian airports has significantly increased, causing long queues and extended wait times for travellers.
Airline passengers have been warned to expect delays at check-in, security and customs as the extra security measures will slow airport processes. Passengers are being told to arrive at domestic airports at least two hours ahead of their expected departure time, and allow three hours for international flights.
The weekend's arrests mark the 13th time Australian authorities have foiled a potential terror attack on home soil since 2014.