Police in Australia have accused two brothers of attempting to smuggle a homemade bomb onto an Etihad plane using explosives sent from Turkey by an Isil commander and then hatching a separate plan to disperse toxic chemicals in a “crowded closed space”.

One of the accused terrorists allegedly planned to plant a bomb in another brother's luggage that would blow up the passenger plane and kill everyone on board.

However, the bag never made it through security and was not checked in, possibly because it was too heavy.

"We will be alleging the person who was to carry the IED on the plane had no idea they were going to be carrying an IED," Michael Phelan, the deputy commissioner of the Australian Federal Police, said on Friday.