ISTANBUL — About a week ago, Iranian President Mahmoud Ahmadinejad declared to the United Nations that most people in the world believe the United States was behind the terrorist attacks of Sept. 11, 2001.

To many people in the West, the statement was ludicrous, almost laughable if it weren't so incendiary. And surveys show that a majority of the world does not in fact believe that the U.S. orchestrated the attacks.

However, the belief persists strongly among a minority, even with U.S. allies like Turkey or in the U.S. itself. And it cannot be dismissed because it reflects a gulf in politics and perception, especially between the West and many Muslims.

"That theory might be true," said Ugur Tezer, 48, a businessman who sells floor tiles in the Turkish capital, Ankara. "When I first heard about the attack I thought, 'Osama,' but then I thought the U.S. might have done it to suppress the rise of Muslims."

A 2006 survey by the Pew Global Attitudes Project found that significant majorities in Egypt, Indonesia, Jordan and Turkey — all among the most moderate nations in the Islamic world — said they did not believe Arabs carried out the attacks.

Two years later, a poll of 17 nations by WorldPublic-Opinion.org, an international research project, found majorities in nine of them believed al-Qaida was behind the attacks. However, the U.S. government was blamed by 36 percent of Turks and 27 percent of Palestinians.

"All this, of course, would require hundreds if not thousands of people to be in on the plot. It speaks volumes for the determination to believe something," said David Aaronovitch, the British author of "Voodoo Histories: the role of Conspiracy Theory in Modern History."