Two Islamic State men facing terrorism charges in Australia were plotting to carry out the country's most sophisticated terror attack on an Etihad Airways flight departing from Sydney last month, police said today. The raids carried by police at five properties in Sydney suburbs had led to arrest of four men. Khaled Khayat and Mahmoud Khayat have both been charged with two terrorism-related offences and were refused bail in Parramatta Local Court today. Another man was released mid- week, while a fourth man remains in custody. The improvised explosive device was intended to be smuggled on a flight on July 15, but the plan was aborted before it reached airport security. Two men were arrested on the charges of planning a terror attack. Australian Federal Police Deputy Commissioner Michael Phelan said Khaled Khayat and Mahmoud Khayat, charged last night with terror offences, had been planning "one of the most sophisticated terror plots attempted on Australian soil". You May Also Want To Watch: Police will allege the IED had been built under instructions from a senior Islamic State (IS) controller in Syria and was to be planted in the luggage of a brother of one of the accused on the Etihad flight out of Sydney on July 15, the Australian Broadcasting Corporation reported. Police said the brother was unaware of the plot. Police described the IED as a "high-end military-grade explosive". However, that attempt was aborted and a second plan was then hatched to create a "chemical dispersion device". Phelan said components and precursor chemicals of the hydrogen sulphide bomb were located during searches on properties in Sydney over the last few days but the plot had now been "completely disrupted". "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," he said. "We do believe that through the wonderful efforts not only of law enforcement but in particular our intelligence agencies that we have completely disrupted this plot."