Story highlights Australian leader said the terror plot was "advanced," but didn't elaborate

Police granted seven days by court to continue interrogating four suspects

Sydney (CNN) Police raided at least five properties in Sydney, Australia, on Monday after four men were arrested over a plan to bring down an airplane as part of a complex terror plot.

Investigators dressed in full protective gear were observed rifling through garbage at the scene and removing items from at least one apartment.

One local resident told CNN he had never seen anything like it in his neighborhood.

Police search for evidence at a block of flats in the Sydney suburb of Lakemba on July 31.

While Australian media was abuzz with theories around the type of the terror device, Australian Federal Police (AFP) commissioner Andrew Colvin said there were no official details had been released as yet.

"The plot that we are investigating we believe was an attempt to put a device onto an aircraft, but beyond that the speculation is just that -- it's speculation," Colvin told a press conference Monday.

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