The famed Sydney Opera House and Harbour Bridge and train stations in Melbourne, where at least four houses were raided by police Wednesday, are believed to have been among the targets, newspapers said on Thursday, quoting unidentified sources.
The raids reportedly followed a 10-month investigation during which officers of the Australian Security Intelligence Organisation (ASIO) tracked a number of known extremists as they made a series of road trips between the two cities.
A spokeswoman for Attorney-General Philip Ruddock told AFP: "ASIO conducted a series of enter and search operations in Melbourne in conjunction with Victoria police and the Australian Federal Police."
"ASIO powers are used judiciously and only under warrant," she said, without giving any further details.
A member of the Melbourne group seen taking video footage of two train stations and the Australian Stock Exchange building told police he needed the footage to help him train as a taxi driver, The Australian said.
The Sydney group had been seen using small boats to spy on the Opera House and Harbour Bridge, The Daily Telegraph reported.
At least four people were questioned in Melbourne and two in Sydney. The raids were planned to disrupt the group to avert possible attacks, and no arrests were made.
The Sydney group had allegedly
been spied on by the accused
Police believe several of the men had undergone paramilitary training in Afghanistan, the reports said.
Australia has already charged several Muslims under terrorism laws adopted since the September 11 attacks on the United States.
They include a Pakistani-born architect accused of planning a bombing campaign and a former airport baggage handler who allegedly compiled an internet terrorism manual.
A British-born convert to Islam, Jack Roche, was jailed for nine years last year after pleading guilty to plotting to bomb Israeli diplomatic missions.
Another Muslim convert, Jack Thomas, was committed to stand trial in April on charges of receiving money from al-Qaida and serving as a "sleeper agent" for the group in Australia.