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On September 11, 2001, then Australian Prime Minister John Howard was in Washington when hijacked planes crashed into the Pentagon, the twin towers of New York's World Trade Center, and a field in Pennsylvania.

"Well, it was quite extraordinary. The sense of shock, and outrage and disbelief was palpable. The other thing I remember though is that the country reacted with remarkable calm," he told SBS.

"This was a more devastating attack on the American homeland than Pearl Harbor. It claimed more lives and, of course, it struck at the heart of both the financial representation of America, as well as its military.

"And it was completely unprovoked. People have to remember that America had not done anything to deserve this, and that added to the sense of outrage and disbelief that people had."

Mr Howard's immediate concern that day was for his wife, Janette, and son, Tim, who were also in Washington and had left the hotel to do some sightseeing.

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The former Prime Minister told SBS his closeness to the tragedy played a role in strengthening his reaction in the aftermath.

"Yes, it had an impact. It always does if you are there and you have a greater understanding of the implications of such an audacious attack.

"And the respect that I had for the way in which Americans responded in a calm but deliberate way was no doubt about their sense of outrage, and there was no doubt they had every right to feel this was a completely unjustified, unprovoked attack on many innocent people. So it did, it left an indelible impression on me, as you might expect."

He again defended criticisms of his decision to follow then US President George Bush and British Prime Minister Tony Blair into war, denying any links drawn between their interventions and the current crisis in the middle east.

"Well certainly, the current conflict with Islamic State is not the result of our intervention in Afghanistan and Iraq. That's an absurd proposition," he said.

"If you study the rise of Islamic State, it burst out of Syria into various parts of Iraq and it is, at least, arguable that if the American withdrawal from Iraq had not been so hasty that there would have been stiffer resistance to Islamic State when it encroached upon Iraq."

Mr Howard became a close friend of Mr Bush, and they are still in contact.

Mr Howard says he isn't concerned about the impact the possible election of controversial Republican nominee, Donald Trump in November, would have on Australia's relationship with the US.

"I think the warmth of the relationship between Australia and the United States will survive any Australian government, any change of Australian government, or any change of the American administration," he said.

"It's based on common values and common commitments to principals of political freedom and liberty, and shared historical experiences. And no matter who the next president of the United States is, that relationship will endure."

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On the 15th anniversary, Mr Howard spoke about the importance of understanding the difference between moderate and extreme Islam.

"Well I don't want anybody vilified on the basis of their religion, that's wrong. But equally, it's pointless ignoring the fact that extreme terrorists used their perverted version of Islam to justify what they do and that is a reality. I think it's unrealistic to ignore that," he said.

"I don't think the result of September 11 was a vilification of Muslims. I think the result of September 11 was a legitimate response to an unprovoked, unjustified attack."

In Australia, Pauline Hanson was this year elected to the senate, with a new focus on Islam, with policies including halting the intake of Muslim refugees, banning the burqa and niqab in public places and holding a Royal Commission into the religion.

Mr Howard said the call for a Royal Commission was "ridiculous".

"Well, I don't think you should have a Royal Commission into any religion," Mr Howard said.

"I don't agree with that at all, but equally Pauline Hanson was voted into the senate by the Australian people and she should be treated with the same respect as any other member of parliament."

Mr Howard declined to give his analysis on whether the Australian government had the right policies to combat current terrorism threats.

"I think the Australian government, and the authorities of this country, are doing a good job in dealing with very difficult threat," Mr Howard said.

"I think, generally speaking, our intelligence agencies are of a high quality. They've probably prevented attacks on Australia and protected this country in ways that we don't even really begin to understand."

"I worry that it might be, that these lone wolf attacks will continue. There's some evidence to suggest that reverses on the battle field for Islamic State and the terrorist groups result in an increase in the number of lone wolf attacks. I hope I'm wrong, but the news evidence to date is not encouraging."