Iranian President Mahmoud Ahmadinejad clashed with a US academic at a forum in New York.
Mr Ahmadinejad insisted in a forum at Columbia University that Iran's nuclear program was purely peaceful. Challenged over his past comments that Israel should be wiped off the map and questioning the Holocaust, he said his concern was why the Palestinians were suffering.
Mr Ahmadinejad received a caustic welcome at the university, which had come under fire from critics who said it should not give a platform to 'a Holocaust denier'.
Security was tight at the hall where he addressed around 700 people, some 80% of them students.
Introducing him, Columbia University President Lee Bollinger said that Mr Ahmadinejad behaved as a 'petty and cruel dictator' and that his Holocaust denials suggested he was either "brazenly provocative or astonishingly uneducated."
Answering questions about his views on the Holocaust, Mr Ahmadinejad said there were no absolutes in academia, and 'a different perspective' was necessary given the impact on the Middle East of those events.
Mr Ahmadinejad also rejected criticism of human rights in his country, notably persecution of homosexuals.
Outside, several hundred protesters objected to his being allowed to speak at the university.
Earlier in a television interview, Mr Ahmadinejad insisted that Iran does not want or need nuclear weapons and that his country was not heading for war with the United States.
He reiterated Iran's position that its nuclear programme is purely peaceful.
In the interview with CBS, Mr Ahmadinejad said his country does not need a nuclear bomb.
Last week Mr Ahmedinejad was denied a request to visit the World Trade Center site of the 11 September attacks.
And while Mr Ahmadinejad said he would not insist on visiting the site if city officials could not arrange it, a visit could still be on the itinerary.
The US is obliged by diplomatic convention and as host of the United Nations to allow representatives of member states to visit areas within 40km of the UN's New York headquarters.
