Iran's hardline President Mahmoud Ahmadinejad has provoked another storm of controversy by claiming many people believe the U.S. government staged the September 11 attacks in an attempt to assure Israel's survival.

His comments prompted the U.S. delegation to walk out of the UN chamber, where he also blamed the U.S. as the power behind UN Security Council sanctions against Iran for its refusal to halt uranium enrichment, a technology that can be used as fuel for electricity generation or to build nuclear weapons.

Delegations from all 27 European Union nations including the UK followed the Americans out along with representatives from Australia, New Zealand, Canada and Costa Rica, an EU diplomat said.

The Iranian leader - who has in the past cast doubt over the US version of the September 11 2001 attacks - also called for an independent fact-finding UN team to be established to probe the attacks. That, he said, would keep the terror assault from turning into what he has called a sacred issue like the Holocaust, where "expressing opinion about it won't be banned".

Ahmadinejad did not explain the logic behind blaming the U.S. for the terror attacks but said there were three theories: One, he said, was that a "powerful and complex terrorist group" penetrated US intelligence and defenses, which is advocated "by American statesmen".

Another, he said, was that "some segments within the U.S. government orchestrated the attack to reverse the declining American economy and its grip on the Middle East in order also to save the Zionist regime. The majority of the American people as well as other nations and politicians agree with this view".

Ahmadinejad said the U.S. used the September 11 attacks as a pretext to invade Afghanistan and Iraq, killing hundreds of thousands of people. He argued that the U.S., instead, should have "designed a logical plan" to punish the perpetrators and not occupy two independent states and shed so much blood, the Press Association reported.