Australia's security chief has warned of the risk of "radicalised" home-grown extremists committing terror acts, adding that "lone wolf" attacks such as occurred in Norway could not be ruled out.
David Irvine, Director-General of the Australian Security Intelligence Organisation (ASIO), said that a decade after the September 11 attacks on the United States, "radicalised" youth posed a realistic threat.
"In terms of current threats, the fact that Al-Qaeda and its associated anti-Western transnational terrorist partners have declared Australia to be a legitimate target of attack continues to be a major concern," he said.
"Of equal concern is that small numbers of Australians have absorbed the ideology of violent religious extremism and have planned or are contemplating and planning acts of terrorism in Australia or overseas.
"This home-grown brand of terrorism, involving mostly young Australians who have been 'radicalised' either by Australian extremists or by overseas inspiration, requires constant vigilance."
In an address late Monday to Adelaide University, Irvine said an event similar to the July bomb and gun attacks which killed 77 people in Norway could not be ruled out in Australia. Far-right extremist Anders Behring Breivik, 32, has confessed to the attacks.
"Particular worries are the so-called 'lone wolf' or 'stand-alone' groups who act independently and throw off few clues as to malicious intent," Irvine said.
He praised the work of Australian authorities, particularly ASIO, in preventing a terror attack on home soil for many years.
"Nevertheless, planning for terrorist attacks on Australian soil has occurred and has been thwarted by ASIO and its law enforcement partners since 9/11," he said.
"Our job is to predict and alert, thereby to prevent the bomb going off."
Irvine, who has headed ASIO since March 2009 and previously led Australia's overseas secret intelligence collection agency (ASIS), said balancing the need to protect the country against personal privacy was a constant concern.
Australia has disrupted four major terror plots since the 9/11 attacks on the United States which killed close to 3,000 people, with 37 of the 38 people prosecuted for those plots being Australian citizens.
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