Four men accused of plotting to bring down a plane planned to use poisonous gas or a crude bomb disguised as a meat mincer, reports said Monday, as stricter screening of passengers and luggage at Australian airports stayed in place indefinitely.

The ramped up security procedures were put in place after four men were arrested at the weekend in raids conducted across several Sydney suburbs.

The men are being held without charge under special terror-related powers.

The Sydney Daily Telegraph said they allegedly planned to carry the device on board a commercial flight from Sydney to a Middle East destination as hand luggage.

It said the idea was to use wood scrapings and explosive material inside a piece of kitchen equipment such as a mincing machine.

The Sydney Morning Herald also reported that a mincer was being examined, while The Australian newspaper cited multiple sources as saying it was a “non-traditional” device that could have emitted a toxic sulfur-based gas.
This, it said, would have killed or immobilized everyone on the aircraft.

But the Australian Federal Police would not confirm the reports.

Prime Minister Malcolm Turnbull also said the plans were “advanced” but refused to comment on the claims over the method of attack. “I have to respect the integrity of the investigations,” he said.

“But I can say that certainly the police will allege they had the intent and were developing the capability.
“There will obviously be more to say over coming days.”

Justice Minister Michael Keenan called the plans “quite sophisticated”.

“It was a plot to bring down an aircraft with the idea of smuggling a device on to it to enable them to do that,” he said.

A magistrate late Sunday gave police an additional seven days to detain the men, who have not been officially named, without charge.

Police continued to gather evidence Monday at the five homes raided, warning the investigation would be “very long and protracted”.

Immigration and Border Protection Minister Peter Dutton told reporters that the alleged plot could prompt longer-term airport security changes.

“The security measures at the airports will be in place for as long as we believe they need to be, so it may go on for some time yet,” said Dutton.

“It may be that we need to look at the security settings at our airports, in particular our domestic airports, for an ongoing enduring period,” he added.