Australian police have made a series of arrests in a counterterrorism operation just days after the country lifted its terror warning to the second-highest level in response to the domestic threat posed by supporters of the Islamic State group.

The Australian Federal Police say officials raided 12 properties across Sydney early Thursday as part of the operation. Police declined to release additional details as the operation was still underway.

Last week, Australian police arrested two men in the eastern city of 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.