(AP) UNITED NATIONS -- The U.S. delegation walked out of the U.N. speech of Iranian President Mahmoud Ahmadinejad on Thursday after he said some in the world have speculated that Americans were actually behind the Sept. 11 terror attacks, staged in an attempt to assure Israel's survival. (Scroll down for video.)

He did not explain the logic of that statement that was made as he attacked the U.S. wars in Iraq and Afghanistan.

Ahmadinejad said there were three theories about the Sept. 11, 2001 attacks:

_ That a "powerful and complex terrorist group" penetrated U.S. intelligence and defenses.

_ "That some segments within the U.S. government orchestrated the attack to reverse the declining American economy and its grips 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."

The Americans stood and walked out without listening to the third theory that the attack was the work of "a terrorist group but the American government supported and took advantage of the situation."

Mark Kornblau, spokesman of the U.S. Mission to the world body, issued a statement within moments of Ahmadinejad's attack.

"Rather than representing the aspirations and goodwill of the Iranian people," he said, "Mr. Ahmadinejad has yet again chosen to spout vile conspiracy theories and anti-Semitic slurs that are as abhorrent and delusional as they are predictable."

WATCH: AHMADINEJAD'S SPEECH

The Iranian leader spoke of threats to burn the Quran by a small American church in Florida to mark the anniversary of the Sept. 11 terror attacks. Although that church backed down, several copycat burnings were posted on the Internet and broadcast in the Muslim world.

"Very recently the world witnessed the ugly and inhumane act of burning the holy Quran," Ahmadinejad said.

He briefly touch on the four sets of sanctions imposed on his country by the United Nations over Tehran's refusal stop enriching uranium and to prove Iran is not trying to build an atomic bomb.

Some members of the Security Council have "equated nuclear energy with nuclear bombs," Ahmadinejad said.

He accused the United States of building up its nuclear arsenal instead of dismantling it and reiterated his call for a nuclear-free world.

"The nuclear bomb is the worst inhumane weapon and which must totally be eliminated. The NPT (Nonproliferation Treaty) prohibits its development and stockpiling and calls for nuclear disarmament," the Iranian president said.