The Iranian president's speech to an overflowing crowd at Columbia University and protests that greeted him overshadowed the annual meeting of the United Nations General Assembly and even the UN chief's push for action on climate change on Monday.
Ahmadinejad was subjected to blistering criticism of his country's human rights record and foreign policy during his Columbia visit and was given a frosty reception by Lee Bollinger, the university's president.
"Mr President, you exhibit all the signs of a petty and cruel dictator," he said.
He also challenged Ahmadinejad's reported denial of the Holocaust."When you come to a place like this it makes you simply ridiculous. The truth is that the Holocaust is the most documented event in human history."
Ahmadinejad rose to applause, and after a religious invocation said Bollinger's opening was "an insult to information and the knowledge of the audience here".
He blamed the university president's "unfriendly treatment" on the influence of the US media and politicians ahead of his visit.
"Many parts of his speech were insults," he said. "We actually respect our students and the professors by allowing them to make their own judgments."
'Evil has landed'
Before his trip and during his Columbia speech and comments to the media on Monday, Ahmadinejad appeared to be reaching out to the American public, giving a much more balanced view than the US media has often portrayed.
But even before his appearance at Columbia, the front page of New York's Daily News already ran the headline "The evil has landed" while The New York Post called Ahmadinejad the "Madman Iran Prez".
Thousands of people gathered outside the United Nations headquarters on Monday to protest against Ahmadinejad's visit.
The speakers, most of them politicians and officials from Jewish organisations, proclaimed their support for Israel and criticised the Iranian leader over remarks questioning the Holocaust.
"We're here today to send a message that there is never a reason to give a hatemonger an open stage," Christine Quinn, speaker of New York City's council, said.
Outside the university lecture hall where Ahmadinejad was to speak, several hundred protesters raised their objections to the event. Some linked arms and sang traditional Jewish folk songs about peace and brotherhood.
Inside, many students were wearing T-shirts with the message "Stop Ahmadinejad's Evil".
Ahmadinejad rejected accusations that he has denied the Holocaust actually happened, but argued for more research to be conducted on the subject.
"I'm not saying that it didn't happen at all," he said. "I said, granted this happened, what does it have to do with the Palestinian people?"
He used his 30-minute speech to repeat Tehran's insistence that its nuclear programme was focused on meeting the country's electricity needs.
Washington says Iran is seeking to produce nuclear weapons.
"We do not believe in nuclear weapons. Period. This goes against the whole grain of humanity," Ahmadinejad said.
During the question-and-answer session he denied that homosexuals were persecuted in Iran.
"In Iran we do don't have homosexuals like in your country. In Iran we do not have this phenomenon. I do not know who has told you we have it," he said, sparking laughter from the audience.
Some, however, were not amused.
"This is a sick joke," said Scott Long of Human Rights Watch, saying Iran tortures gays under a penal code that punishes homosexuality between men with the death penalty.
US targets Iran force
Separately, Condoleezza Rice, the US secretary of state, ratcheted up the pressure on Tehran, telling the Reuters news agency that the US was considering sanctions against the entire al-Quds force of Iran's Revolutionary Guard.
Such a designation would enable Washington to target the force's financing.
The US accuses the Quds force of inciting violence in Iraq and of training and equipping fighters who have attacked US troops.
Iran has repeatedly denied this.
The US is increasing diplomatic pressure on Iran to stop uranium enrichment, which can produce nuclear weapons, and targeting the al-Quds force would be part of that strategy.
"Remember that the problem with the Quds force is that it has a network of activities in support of terrorism but it also, we believe, has a network of activities in support of proliferation," Rice said.
'Occupation and racism'
On Monday morning, Ahmadinejad met leaders of a movement called Neturei Karta International.
The Orthodox Jewish group believes that Jews are forbidden to have their own state until the coming of the Messiah and are therefore opposed to the existence of the state of Israel.
Afterwards, in a video conference with reporters in Washington, Ahmadinejad accused Israel of occupation and racism.
"It constantly attacks its neighbours," he said. "It kills people. It drives people from their homes."
Ahmadinejad is due to address the United Nations General Assembly on Tuesday.
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