About 800 federal and state police officers raided more than a dozen properties across Sydney as part of the operation '€” the largest in Australian history, Australian Federal Police Deputy Commissioner Andrew Colvin said. Separate raids in the eastern cities of Brisbane and Logan were also conducted.

One person was charged with serious terrorism-related offenses and was scheduled to appear in court later Thursday. Colvin declined to detail the exact nature of the charges.

The arrests come just days after the country raised its terror warning to the second-highest level in response to the domestic threat posed by supporters of the Islamic State group.

"Police believe that this group that we have executed this operation on today had the intention and had started to carry out planning to commit violent acts here in Australia," Colvin said. "Those violent acts particularly related to random acts against members of the public. So what we saw today and the operation that continues was very much about police disrupting the potential for violence against the Australian community at the earliest possible opportunity."

Police declined to reveal exact details of the attack they believe was being plotted. New South Wales Police Commissioner Andrew Scipione said only that it was to be carried out against a member of the public on the street and was at "a very high level."

"Right now is a time for calm," Scipione said. "We need to let people know that they are safe, and certainly from our perspective, we know that the work this morning will ensure that all of those plans that may have been on foot have been thwarted."

Last week, Australian police arrested two men in Brisbane for allegedly preparing to fight in Syria, recruiting jihadists and raising money for the al-Qaida offshoot group Jabhat al-Nusra, also known as the Nusra Front.

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