The Iranian president, Mahmoud Ahmadinejad, has triggered a diplomatic furore over his request to lay a wreath at the World Trade Centre site to commemorate the September 11 attacks.

Even before setting foot on US soil for the upcoming UN general assembly, the Iranian leader has managed to ruffle American feathers by asking to visit what is considered a sacred site.

Mr Ahmadinejad, who is to due to arrive on Sunday to address the assembly, had asked New York city and the US secret service earlier this month for permission to visit Ground Zero.

A statement by the New York police commissioner, Raymond Kelly, that said the city was considering the application, prompted outrage from politicians, quickly resulting in a refusal.

Rudy Giuliani, who was mayor during the attacks and is now a Republican presidential candidate, branded Mr Ahmadinejad's request "outrageous" and described him as "a man who has made threats against America and Israel; is harbouring [Osama] bin Laden's son and other al-Qaida leaders; is shipping arms to Iraqi insurgents; and is pursuing the development of nuclear weapons".

Hillary Clinton, the Democratic presidential candidate, said it was "unacceptable" for Mr Ahmadinejad "to visit the site of the deadliest terrorist attack on American soil in our nation's history".

Mohammad Mir Ali Mohammadi, a spokesman for the Iranian mission to the UN, described the refusal as unfortunate.

"President Ahmadinejad intended to lay a wreath at the site of Ground Zero in order to pay tribute to the victims of the terrorist attacks of September 11 2001. We are hopeful that we can still work something out with the police department."

Mr Ahmadinejad is scheduled to speak at Columbia University on Monday at a forum of world leaders organised by the college's school of international and public affairs. It promises to be a raucous affair.

The Iranian leader has been dogged by protesters during past visits. A year ago, after he was invited to address the same Columbia forum, the invitation was withdrawn because his appearance might not "reflect the academic values of the event".

The president's visit to the US comes amid intense speculation of a possible American strike at Iran's nuclear facilities over Tehran's refusal to halt its uranium enrichment programme.

The US is trying to drum up support for a third round of UN sanctions against Iran, with France on board, but with Russia and China reluctant to pressure Iran further.

Apart from the nuclear issue, Washington has stepped up accusations against Iran over its alleged support for Shia militants in Iraq who are targeting American soldiers with explosive devices.

In a television appearance earlier this week, Mr Ahmadinejad said his country wanted peace and friendship with the US, despite mounting tensions.

The US has also denied a visa to Iran's UN ambassador in Geneva to attend next week's general assembly meeting because he was allegedly involved in the 1979 US hostage crisis in Tehran, a UN official said.