A US national intelligence estimate from April said the Iraq war had spawned a new generation of Islamic radicals and made the terrorism problem worse, according to a report in the New York Times newspaper.
However, Mr Howard says that global terrorism had been a problem since well before the invasion of Iraq.
"My response is that there are many theories about the origins of terrorism and the factors that bear on terrorism," he said.
"One fact is absolutely certain, and that is that Australia and the United States and many other countries were terrorist targets long before the military operation in Iraq.
"I remind you that the 88 Australians who were killed in Bali were murdered before the invasion of Iraq.
"And I remind you that the first attack on the World Trade Centre took place in 1993, ten years before the military operation in Iraq."
Mr Howard said the leaked document was another contribution to the debate on terrorism.
"I think it's just another contribution to a debate that will go on for a long period of time," he said.
"It's another view. You've asked me my view, I've given you my view."