On the fifth anniversary of terrorists flying hijacked planes into the World Trade Centre and the Pentagon, new US ambassador Robert McCallum will host the memorial service at the embassy in Canberra.
Prime Minister John Howard, who was in Washington at the time of the attacks, has admitted he fears a similar attack on towering office blocks in downtown Sydney.
Mr Howard, who will attend today's service, says the government has the power to order the Australian air force to shoot down a hijacked plane in the event of a similar attack but said he hoped it would never be needed.
Mr Howard said he often looked at Sydney's skyscrapers and contemplated the consequences of a major terrorist attack during his regular morning walks.
"An attack on a major sporting event, a plane, a big building. Every time I go for a walk in the morning I see those buildings and thoughts go through my head. I have to be honest and say that," he said.
Opposition Leader Kim Beazley says the government has not done everything it can to protect Australia from an attack.
But Justice Minister Chris Ellison said the government had spent more than $8 billion on a range of initiatives to protect against terrorist attacks over the past decade.
Howard on Muslims
Meanwhile Mr Howard has told the ABC’s Four Corners program that a section of Australia's Muslim community does not share Australian values and will not integrate into the Australian community.
Mr Howard told the program which marked the fifth anniversary of the September 11 terror attacks that the rest of the Muslim community needed to make sure these people did not have adverse consequences for all and he added he was concerned about the potential influence of some people on young Muslim men.
"There is a section of the Islamic population which will not integrate ... does have values and attitudes which are hostile to Australia's interests, and I have said that before," he said.
"And I would like the rest of the Islamic community to join the rest of the Australian community in making sure that the views and attitudes of that small minority do not have adverse consequences."