Australian authorities carried out raids Thursday, making arrests in connection with a horrifying terror plot by ISIS.

More on the plot from FoxNews.com:

Australian counterterrorism forces detained 15 people Thursday in a series of suburban raids after receiving intelligence that the Islamic State militant group was planning public beheadings in two Australian cities to demonstrate its reach.

About 800 federal and state police officers raided more than a dozen properties across 12 Sydney suburbs as part of the operation -- the largest in Australian history, Australian Federal Police Deputy Commissioner Andrew Colvin told the Associated Press. A sword was removed as part of evidence at one of the homes.

Separate raids in the eastern cities of Brisbane and Logan were also conducted.

The Australian Broadcasting Corporation reported that the plan involved kidnapping randomly selected members of the public off the streets in Sydney and Brisbane, beheading them on camera, and releasing the recordings through Islamic State's propaganda arm in the Middle East.

Later Thursday, Attorney General George Brandis confirmed that a person born in Afghanistan who had spent time in Australia and is now working with the Islamic State group in the Middle East ordered supporters in Australia to behead people and videotape the killings.

"If the ... police had not acted today, there is a likelihood that this would have happened," Brandis told the Australian Broadcasting Corporation.

House Homeland Security Committee Chairman Rep. Michael McCaul (R-TX) reacted to the brutal plan this morning, telling Bill Hemmer that the plot demonstrates the threat posed to the world by ISIS.

He said one plot involved the beheadings and another involved bombing with IEDs the equivalent of FBI headquarters in Australia.

McCaul said intelligence officials are looking into whether this plot was being directed out of Syria by ISIS leader Abu Bakr al-Baghdadi or whether it was Islamic extremists acting on their own.

Hemmer noted that the plot calls to mind last year's brutal murder of a British soldier on a London street.

Watch the full interview above.