Ahmadinejad told the U.N. audience that the United States used "the mysterious September 11 incident" as a pretext for wars against Afghanistan and Iraq.
The Iranian president offered his criticism in the form of a series of questions, asking who had engaged in slavery, imposed colonialism, supported military regimes and triggered World War I, World War II, the Korean War and the Vietnam War.
"The answers are clear," Ahmadinejad said.
"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," he said.
The two U.S. diplomats, who specialize in the Middle East, were followed out of the chamber by diplomats from more than 30 countries. They included the 27 European Union members, Australia, New Zealand, Somalia, Liechtenstein, Monaco, San Marino and Macedonia, a U.N. diplomat said.
Mark Kornblau, spokesman for the U.S. Mission to the United Nations, said: "Mr. Ahmadinejad had a chance to address his own people's aspirations for freedom and dignity, but instead he again turned to abhorrent anti-Semitic slurs and despicable conspiracy theories."
Ahmadinejad accused some unidentified European countries of still using the Holocaust "as the excuse to pay fine or ransom to the Zionists." He also said any question about the foundation of Zionism is condemned by the U.S. "as an unforgivable sin."
When the idea of an independent fact-finding investigation of "the hidden elements" involved in the Sept. 11 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.
Later, in an interview with The Associated Press, Ahmadinejad said the World Trade Center towers collapse couldn't have been just due to the planes, but explosives must have been detonated.
Ahmad Batebi, an Iranian human rights activist who fled the country in 2008 after years of imprisonment, said the problem is the oppressive Iranian regime, not Ahmadinejad.
"Ahmadinejad is not important," Batebi told msnbc.com. "He is a temporary person in his position." The message he brought to the U.N. was "just the Iranian government, not the Iranian people," he said.
Ahmadinejad spoke one day after two Americans were released by Iran after being convicted of spying and being held for two years.
Josh Fattal and Shane Bauer, who said they had been hiking along the Iran-Iraq border, arrived Wednesday in Oman under a $1 million bail-for-freedom deal and were embraced by relatives. Also on hand was Sarah Shourd, who was freed by Iran last year.
Story: Freed US hikers spend 1st day of freedom secluded with kin
The three were detained in July 2009 along the Iran-Iraq border. They maintained their innocence, saying they were only hiking in Iraq's relatively peaceful Kurdish region and might have accidentally wandered into Iran. Last month, Fattal and Bauer were sentenced to eight years in prison each for illegal entry into Iran and espionage.
The Associated Press and Reuters contributed to this report.
I suppose it was all about the 'risk of appearing rude', versus, the act of having your nose rubbed in it! I guess rudeness won the day.
Its a pity those 30 others had to follow. They're not playing 'follow the leader', so much as, follow the bully in charge.