Sydney, London- Australian Federal Police said a senior ISIS commander sent parts to construct an improvised explosive device (IED) for the two men arrested for their attempt to bring down Etihad Airways flight coming from Sydney Airport.

According to CNN, the two suspects are: Khaled Khayat and Mahmoud Khayat.

“This is one of the most sophisticated plots that have ever been attempted on Australian soil,” Australian Federal Police Deputy Commissioner Michael Phelan said.

“We’ll be alleging that the person who was to carry the IED on the plane had no idea he was going to be carrying an IED,” Phelan said. “I want to make it quite clear – it never got near screening. I don’t want anyone to suggest that it penetrated airport security layers because it did not,” Phelan added.

Abu Dhabi’s Etihad Airways said on Friday it was helping Australian Federal Police with an investigation, that the police began, into a plot to bring down a plane, resulting in stricter security screening at Australian airports.

Four men were arrested in several suburbs in Sydney Saturday on charges of planning for the attack inside the airplane.

US officials, who spoke to Reuters on condition of anonymity, said a foreign intelligence service had intercepted communications between the plotters in Sydney and members of the ISIS in Syria – the officials declined to identify the foreign intelligence service.

Another US official said the target appeared to have been a commercial flight from Sydney to the Gulf.

Australia is an ally of US and has dispatched forces to Afghanistan and Iraq – it has been in a state of alert since 2014 following attacks by extremists returning from the Middle East.