NEW YORK (AP) – Iranian President Mahmoud Ahmadinejad took the stage at Columbia University today to a blistering reception from the president of the school, who said the hard-line leader behaved like "a petty and cruel dictator."

Ahmadinejad smiled as Columbia President Lee Bollinger took him to task over Iran's human-rights record and foreign policy, and Ahmadinejad's statements denying the Holocaust and calling for the disappearance of Israel.

"Mr. President, you exhibit all the signs of a petty and cruel dictator," Bollinger said, to loud applause.

He said Ahmadinejad's denial of the Holocaust might fool the illiterate and ignorant.

"When you come to a place like this it makes you simply ridiculous," Bollinger said. "The truth is that the Holocaust is the most documented event in human history."

Ahmadinejad rose, also to applause, and after a religious invocation, said Bollinger's opening was: "an insult to information and the knowledge of the audience here."

"There were insults and claims that were incorrect, regretfully," Ahmadinejad said, accusing Bollinger of falling under the influence of the hostile U.S. press and politicians.

"I should not begin by being affected by this unfriendly treatment," he said.

During a question and answer session with the audience, Ahmadinejad appeared agitated. In response to one question, Ahmadinejad denied he was questioning the existence of the Holocaust.

"Granted this happened, what does it have to do with the Palestian people?" he said.

But then he said he was defending the rights of European scholars, an apparent reference to a small number who have been prosecuted under national laws for denying or minimizing the Holocaust. "There's nothing known as absolute," he said.

During his prepared remarks, the Iranian president did not address Bollinger's accusations directly, instead launching into a long religious discursion laced with quotes with the Quran before turning to criticism of the Bush administration and past American governments, from warrantless wiretapping to the bombing of Hiroshima and Nagasaki.

Bollinger was strongly criticized for inviting Ahmadinejad to Columbia, and had promised tough questions in his introduction to Ahmadinejad's talk. But the strident and personal nature of his attack on the president of Iran was startling.

"You are either brazenly provocative or astonishingly uneducated," Bollinger told Ahmadinejad about the leader's Holocaust denial. "Will you cease this outrage?"

Ahmadinejad said he simply wanted more research on the Holocaust, which he said was abused as a justification for Israeli mistreatment of the Palestinians.

"Why is it that the Palestinian people are paying the price for an event they had nothing to do with?" Ahmadinejad asked. He closed his prepared remarks with a terse smile, to applause and boos, before taking questions from the audience.

President Bush said Ahmadinejad's appearance at Columbia "speaks volumes about really the greatness of America."

He told Fox News Channel that if Bollinger considers Ahmadinejad's visit an educational experience for Columbia students, "I guess it's OK with me."

Thousands of people jammed two blocks of 47th Street across from the United Nations to protest Ahmadinejad's visit to New York. Organizers claimed a turnout of tens of thousands. Police did not immediately have a crowd estimate.

The speakers, most of them politicians and officials from Jewish organizations, proclaimed their support for Israel and criticized the Iranian leader for his 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," New York City Council Speaker Christine Quinn said.

Protesters also assembled at Columbia. Dozens stood near the lecture hall where Ahmadinejad was scheduled to speak, linking arms and singing traditional Jewish folk songs about peace and brotherhood, while nearby a two-person band played "You Are My Sunshine."

Signs in the crowd displayed a range of messages, including one that read "We refuse to choose between Islamic fundamentalism and American imperialism."

Associated Press writers Karen Matthews and Aaron Clark contributed to this report.