Two men accused of a terror plot to bring down a plane with a bomb were also trying to build a device that could release toxic gas, Australian police allege.
A police officer at a checkpoint in the Sydney inner suburb of Surry Hills. Photo: AFP
The first plot involved placing an improvised explosive device on an Etihad flight out of Sydney on 15 July, according to Australian Federal Police.
The other, a gas "dispersion" device, was not close to fruition, police said.
Investigators said the alleged plots had been "completely disrupted".
"This is one of the most sophisticated plots that has ever been attempted on Australian soil," said Deputy Commissioner Michael Phelan.
Mr Phelan said the first plot involved a "high-end" military-grade explosive, but it did not get through check-in.
"There is a bit of conjecture [about] why it did not get through the baggage check-in, but I want to make it quite clear - it never got near [security] screening," he said.
The components of the explosive were allegedly sent from Turkey by an senior figure within so-called Islamic State (IS).
They were transported to Australia via air cargo, he said.
The second alleged plan involved creating an improvised chemical device that was designed to release toxic hydrogen sulphide, or "rotten egg gas".
However, Mr Phelan said that plan was not close to being realised when police conducted raids on Saturday and arrested four men.
A court hearing took place in a Sydney on Friday with the two men charged with "preparing for, or planning, a terrorist attack".
Another man was released on Tuesday while the fourth remains in police custody.
Police allege one of the men who has been charged was put in contact with an IS figure in April.
Police have spent the week gathering evidence following the raids in the Sydney suburbs of Lakemba, Punchbowl, Surry Hills, Wiley Park and Bankstown.
On Thursday, Prime Minister Malcolm Turnbull said the suspected plot had been "disrupted and contained".
- BBC