2 Australian men charged over foiled terror plot to bring down airplane The men were charged in connection to an alleged plot to bring down an airplane.

 -- Two Australian men were charged Thursday night in connection with a foiled plot to bring down an airplane, officials said.

The two men, ages 49 and 32, were each charged with two counts of acts done in preparation for, or planning, a terrorist act. Both are from suburbs of southwestern Sydney, authorities said.

The two suspects are scheduled to appear at Parramatta Court House on Friday morning.

On Saturday, Australian authorities arrested a total of four men in Sydney over allegations about a potential terrorist attack. The attack was allegedly planned to be carried out aboard an airplane using an improvised device, one that was likely designed to be hidden inside a "meat grinder," according to the U.S. State Department.

A 50-year-old man was released from police custody without charge on Tuesday.

One man remained in custody Thursday night under the country's "specified time" provisions, which allow for extended detention of suspects in terrorism investigations, according to the Australian Federal Police.

At a press conference in Perth on Wednesday, Australian Prime Minister Malcolm Turnbull said there was no longer any threat to the country's aviation industry and that the aviation threat level would be restored to its previous level.

"The threat to aviation from the plot that was uncovered to bring down a plane has been disrupted and contained," Turnbull told reporters. "The police have uncovered very substantial evidence."

The Australian Federal Police have conducted searches at six properties across Sydney this week, including in the suburbs of Lakemba, Punchbowl, Surry Hills, Wiley Park and Bankstown. The investigation is ongoing.

If found guilty, the two men could each receive a maximum penalty of life imprisonment, according to the Australian Federal Police.

ABC News' Benjamin Gittleson and Joshua Hoyos contributed to this report.