In a wide-ranging interview Thursday evening with The Associated Press, Ahmadinejad, on the Sept. 11 attacks, stopped short of saying the United States staged the disaster 10 years ago.

He said that as an engineer, he's sure "this was a systematic collapse of those towers." "I can say with certainty there must have been explosive material that was set off in sequence," he said. He reiterated his call for an independent investigation, noting there are doubters in the United States as well. "A few airplanes without previous coordination known to the security forces and the intelligence community in the United States cannot become missiles and target the heart of the United States," Ahmadinejad said.

A six-year investigation by The National Institute of Standards and Technology found that extreme heat from the jetliner crashes in the twin towers caused some steel beams to lose strength, causing further failures in the building until the entire structure succumbed.