IS commander directed foiled Australia-Etihad bomb plot: Police

A senior Islamic State (IS) group commander directed a group of Australian men to build a bomb destined for an Etihad Airways passenger plane out of Sydney, police alleged on Friday.

The improvised explosive device was due to be smuggled onto the 15 July flight, but the attempt was aborted before they reached security. Two men have been charged, with a third still being questioned.

"This advice was coming from a senior member of the Islamic State," Australian Federal Police Deputy Commissioner Michael Phelan said, referring to him as a "commander" based overseas.

Police also foiled a second alleged plot involving a "chemical dispersion device," designed to release highly toxic hydrogen sulphide, but this plan was in the early stages.

"Not only have we stopped the IED that was believed to go on the plane but we have also completely disrupted the intended chemical dispersion device," said Phelan.

The IS leader sent components through international cargo to the men, then directed them on how to build a bomb, police said.

US officials told Reuters on Tuesday that a foreign intelligence service had intercepted communications between the plotters in Sydney and members of the IS group in Syria. The officials declined to identify the foreign intelligence service.

Two other US officials familiar with the Australian arrests said a developing plot had been detected. One of them, also speaking on condition of anonymity, said the alleged plot was "fairly well along" when it was disrupted by Australian authorities.

The other official said the target appeared to have been a commercial flight from Sydney to the Gulf.

"With assistance from the ISIL commander, the accused assembled the IED into what we believe was a functioning IED to be placed on that flight," said Phelan.

"There is a little bit of conjecture as to why it didn't go ahead. It didn't get past the check-in."

Phelen referred to it as "one of the most sophisticated plots that has ever been attempted on Australian soil".

Four men were arrested during raids in Sydney on Saturday. 

Two of them - aged 32 and 49 and reportedly brothers - were each charged late Thursday with two counts of "acts done in preparation for, or planning, a terrorist act" and are due in court on Friday.

One man has been released without charge and another is still being questioned.

Sydney's Daily Telegraph reported that an Etihad flight to Abu Dhabi, which could have carried up to 500 people, was the target.

The paper identified one of the suspects as local butcher Khaled Khayat.