President Mahmoud Ahmadinejad has left Iran for the United States, where he is due to address the UN General Assembly in New York.
Mr Ahmadinejad's trip has already created controversy over his calls for the destruction of Israel and his questioning of the scale of the Holocaust.
Columbia University was urged to withdraw a speaking invitation to the Iranian president during his trip to New York.
Columbia University's website says the forum aims to foster public debate on key economic, political and social questions.
Meanwhile, New York police have denied Mr Ahmadinejad's request to visit the World Trade Center, site of the 11 September attacks.
Mr Ahmadinejad has he was amazed by the reaction to his proposed visit to Ground Zero and he would try to go if he have the time and the conditions are conducive.
Asked in an interview with CBS's 60 Minutes if he would press his request, he said that if local officials could not make the necessary arrangements, he said he would not insist.
President George W Bush, asked to comment on the decision not to allow the visit to the World Trade Center site, said he could understand why officials in New York would not want somebody that is running a country who is a state sponsor of terror at the site.
In 2002, Bush labelled Iran as part of an axis of evil that also included Iraq and North Korea and has accused it of backing international terrorist groups.
The US and other Western powers also say Iran is trying to develop nuclear weapons. Iran insists it wants nuclear technology only for civilian electricity generation.
