Australian police said they had raided a number of properties around the southern city of Melbourne on Tuesday, part of a security crackdown on radical Islamists authorities believe are planning attacks in the country.
Australia, which is backing the United States and its escalating action against Islamic State in Syria and Iraq, is on high alert for attacks by radicalized Muslims or by home-grown militants returning from fighting in the Middle East.
Last week, an 18-year-old identified as Abdul Numan Haider was shot and killed by counter-terrorism police in the Melbourne suburb of Endeavour Hills after he attacked them with a knife.
"This operational activity is not in response to a threat to public safety nor is it related to last week's incident at Endeavour Hills," Australian Federal Police said in a statement about the raids in five Melbourne suburbs on Tuesday.
The Australian Broadcasting Corp. said one man had been arrested. Police said they would not comment further while the operation was under way.
Earlier this month, more than 800 officers were involved in a security operation in Sydney and Brisbane, which authorities said had thwarted a plot by militants linked to Islamic State to behead a random member of the public.
Australia is concerned over the number of its citizens believed to be fighting with militant groups overseas, including a suicide bomber who killed three people in Baghdad in July and two men shown in images on social media holding the severed heads of Syrian soldiers.
Australian Prime Minister Tony Abbott has said at least 100 Australians are in the Middle East either fighting with or supporting Islamic State or other militant groups, a number that he said has increased in recent months.
At least 20 are believed by authorities to have returned to Australia and pose a security risk, and some 60 people have had their passports cancelled. Earlier this month, the national security agency raised its four-tier threat level to "high" for the first time.
Prominent Australian Muslims say their community is being unfairly targeted by law enforcement agencies and threatened by right-wing groups because the government's tough policies aimed at combating radical Islamists threaten to create a backlash.
Australia has deployed troops and aircraft to the Middle East in preparation to join a US-led coalition which has begun strikes against Islamic State militants. The Australian government is expected to sanction involvement of its forces in action in Iraq as early as Tuesday.