The terrorist plot to bring down an airplane, uncovered by Australian anti-terrorism police over the weekend, was “very sophisticated” and well advanced, the country’s government said Monday.

Two fathers and their sons were reported to be the four men arrested in Sydney over an Islamist plot to blow up a plane.

The men were still being questioned Monday by police in Sydney after being arrested by heavily armed officers during raids on their homes Saturday evening.

The men were related by marriage, the Daily Telegraph newspaper reported.

The plot to bring down a plane was advanced before police swooped in, Prime Minister Malcolm Turnbull said Monday on local broadcaster ABC radio.

“It will be alleged that this was an Islamist, extremist terrorist motivation,” Turnbull said.

Police had uncovered “a very sophisticated plot” that would have taken “extensive planning,” Justice Minister Michael Keenan said.

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Keenan claimed it was the thirteenth time that authorities have stopped a terror attack in the country.

A home-made bomb was apparently found in an inner city terrace home, possibly to be planted on a commercial passenger flight from Sydney to the Middle East, the Sydney Morning Herald reported.

Investigators believe that because of the sophistication of the plot, the men might have had some overseas direction, the paper reported.

The plan involved using wood scrapings and explosive material inside a piece of kitchen equipment, such as a meat mincing machine that police were seen removing from one of the homes, the Telegraph reported.

Police have gained court permission to extend the interrogation period to seven days.

In the wake of the disrupted plot, air passengers faced long lines at Sydney’s domestic airport terminal on Monday morning, with boosted security checks.

The lines mostly cleared up by midday, however, and most flights were now departing on time, the Herald reported. (NAN)