The United States said Wednesday it was "speechless" after Iranian President Mahmoud Ahmadinejad voiced doubts about the accepted version of the September 11, 2001 attacks on New York and Washington.

"I am not sure what you say about a statement like that. It leaves one speechless," said State Department spokesman Sean McCormack.

"It is just misguided, misinformed rhetoric," McCormack said.

"I cannot tell whether or not it is something that he truly believes or if this is just an attempt to try to shake up public opinion in Iran or elsewhere," McCormack said.

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Earlier Wednesday, Ahmadinejad called the 9/11 attacks a "suspect event" in a speech at a public rally in the holy city of Qom.

"Four or five years ago a suspect event took place in New York," Ahmadinejad said, in an address carried live on state television.

"A building collapsed and they said that 3,000 people had been killed, whose names were never published."

"Under this pretext they (the United States) attacked Afghanistan and Iraq and since then a million people have been killed," said the Iranian president.

This was the third time in just over a week that Ahmadinejad has publicly raised doubts about the September 11 airborne attacks on New York and Washington carried out by Al-Qaeda militants which killed nearly 3,000 people.

He raised the theme for the first time at a ceremony on April 8, Iran's national day marking its disputed nuclear program, which the West fears could be used to make nuclear weapons.

The president of Iran at the time of the 9/11 attacks, Mohammad Khatami, strongly condemned the assault. Tehran did not oppose the US-led invasion of Afghanistan that toppled the Taliban regime, which was hostile to the Iranian government.