Commercial flight from Sydney to the Gulf said to be the target amid claims the four men arrested had links to Isis

This article is more than 3 years old

This article is more than 3 years old

A terrorist plot to bring down a plane was “fairly well along” when Australian authorities moved in, US officials say, amid claims the four men arrested over the plan had links to Islamic State.

The men, named in media reports as father and son Khaled and Mahmoud Khayat, and Khaled and Abdul Merhi, remain behind bars and are yet to be charged after being arrested on Saturday.

Khaled Khayat’s brother is believed to be a senior Isis figure, while the other two men are related to Ahmed Merhi, who travelled to Syria in 2014, the ABC reported.

Australian federal police have not elaborated on the details of the plan to “bring down” a plane and will not confirm if a series of raids in Surry Hills, Lakemba, Wiley Park and Punchbowl were triggered by overseas intelligence alerts.

Huge airport delays in Sydney and Melbourne amid heightened security Read more

Reuters has cited two US officials familiar with the arrests as saying the Australian investigation was not a sting operation but the result of the detection of a developing plot.

One said it was “fairly well along” when Australian authorities disrupted it. The target, the other official said, appeared to have been a commercial flight from Sydney to the Gulf.

Two other US officials, also speaking on condition of anonymity, said communications between the alleged plotters in Sydney and members of Isis in Syria were intercepted by a foreign intelligence service.

The US officials declined to identify the service and UK officials refused to confirm or deny playing a role in detecting the plot.

Facebook Twitter Pinterest Police carry items from the scene of a terrorism raid in Lakemba on Sunday. Photograph: Getty Images

Travellers at Australian airports were due to face another day of delays on Tuesday amid heightened security screenings.

The Australian National University criminologist Clarke Jones said the federal government needed to go “back to basics” and invest in prevention measures.

“It’s been full-steam ahead in relation to security, legislation, police and intelligence, all at the expense of community resilience and building up protective mechanisms within vulnerable communities,” he said.

The men are being held in Sydney under counter-terrorism legislation that grants authorities the power to keep people in custody as evidence is gathered to support any charges.