A staunch US ally, Australia has been on heightened alert for attacks by home-grown radicals, having suffered several "lone wolf" assaults, including a cafe siege in Sydney in 2014 in which two hostages and the gunman were killed and an attack by an "Islamic State-inspired" 22-year-old man on Sunday.
Australia has also sought to tighten oversight of potential threats by lowering the age of people who can be subjected to telecommunications interceptions and searches to 14.