Iranian president Mahmoud Ahmadinejad has outraged the UN by calling the 9/11 attack on the U.S. “a mystery”.

The claim so angered the U.S., coming barely a week after the 10th anniversary of the terrorist attacks, that the entire American delegation walked out while Ahmadinejad was still speaking, Daily Mail reported.

In a speech full of questions which were no more than thinly veiled attacks on the U.S. he asked the UN who had used the “mysterious September 11 incident” as a precursor to war and to dominate the Middle East?

He added: “By using their imperialistic media network which is under the influence of colonialism they threaten anyone who questions the Holocaust and the September 11 event with sanctions and military actions.”

When the idea of an independent fact-finding investigation of “the hidden elements” involved in the attacks was raised last year, he said, “my country and myself came under pressure and threat by the government of the United States.”

“Instead of assigning a fact-finding team, they killed the main perpetrator and threw his body into the sea,” Ahmadinejad said, referring to the U.S. military's killing of Al-Qaida leader Osama bin Laden in early May.

Ahmadinejad then went on to accuse NATO of sanctioning drug trafficking, claiming that production of illegal drugs has increased despite NATO's “occupation”.