(Bloomberg) —Two men will appear in an Australian court on Friday charged over an alleged plot to bring down an Etihad Airways PJSC flight last month with a homemade bomb.

The Australian Federal Police allege the two men, aged 49 and 32, attempted to smuggle an improvised explosive device onto the flight from Sydney on July 15, but didn’t get through check-in. When that plot failed, officers allege the men took the bomb apart and planned to turn it into a device that could disperse dangerous chemicals.

The military-grade explosives, which originated in Turkey, were allegedly sent to Australia on a cargo flight by Islamic State militants, police said.

“This is one of the most sophisticated plots that has ever been attempted on Australian soil,” AFP Deputy Commissioner Michael Phelan told reporters Friday. “We could very well have had a catastrophic event.”

Counter-terrorism police raided several Sydney suburbs on Saturday after uncovering the plot, which was allegedly inspired by the militant group Islamic State. Four men were arrested and authorities tightened security at all major international and domestic terminals across Australia.

A 50-year-old man was released from custody earlier this week and another man remains in custody without being charged.

Police say the men were a long way from having a “functioning chemical dispersal device” and the plot was completely disrupted.