Terror suspects planned TWO attacks: one in the air, the other on public transport.

A Sydney-based terror plot to bring down a plane included an aborted attempt to place an improvised explosive device on an Etihad flight out of Sydney on July 15.

Australian Federal Police deputy commissioner Michael Phelan on Friday said at no point did the IED breach airport security.

“It did not get through security,” he told reporters.

There was a second terror plot related to the building of an improvised chemical dispersion device to release colourless toxic gas – possibly on public transport according to The Age.

“It was designed to release the highly toxic hydrogen sulfide,” Mr Phelan said, but he stressed the alleged conspirators “were a mile-and-a-half from having a functioning chemical dispersion device”.

Police say two men arrested on terror offences were allegedly planning another attack involving hydrogen sulphide. https://t.co/fA7o4xF4eK

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Two men will face a Sydney court on Friday in relation to the plot.

A 49-year-old from Lakemba and a 32-year-old from Punchbowl on Thursday night were each charged with two counts of acting in preparation for, or planning, a terrorist act.

They face a maximum penalty of life imprisonment.

A third man remains behind bars, held under special anti-terror laws, while police investigations continue. He can be detained until the weekend under the current ruling.

Mr Phelan said the aborted July 15 attempt involved a high-end explosive being concealed in a meat grinder.

Police will allege the 49-year-old carried the device to Sydney’s international airport in the hope of putting it on the plane in “checked luggage”.

“This is one of the most sophisticated plots that has ever been attempted on Australian soil,” Mr Phelan said.

“If it hadn’t been for the great work of our intelligence agencies and law enforcement over a very quick period of time then we could well have a catastrophic event in this country.”

The parts for the IED came from Turkey, police say.

It’s alleged a senior Islamic State member sent the components to Australia by air cargo where it was assembled into an explosive device.

Authorities are confident they’ve now found “every single component of that IED”.

“One of the two gentlemen charged, the brother we’re alleging is a senior member of ISIL in Syria and he indeed introduced another person, who we call the controller, to one of the people that has been charged,” Mr Phelan said.