The scene is set for a clash of the "Great Satan" and the "axis of evil" at the United Nations this month when presidents George W. Bush and Mahmoud Ahmadi-Nejad address the general assembly on the same day, with the US pressing the world body to impose sanctions on Iran over its nuclear programme.

The White House confirmed yesterday that the Iranian president would be granted a US visa to go to New York. "This will be the debate," a US official said, referring to Mr Ahmadi-Nejad's challenge to Mr Bush to hold a televised debate.

According to the UN agenda, Mr Bush is due to speak ahead of the Iranian president on September 19, the official noted.

Mr Ahmadi-Nejad attended the general assembly last year shortly after his election victory but only after US officials raised questions over his visa application following allegations - never substantiated - that he had played a role in the 1979-81 US embassy hostage crisis in Tehran.

Since then Mr Ahmadi-Nejad has been widely condemned for questioning the Holocaust and calling for Israel to be wiped off the map by Palestinians. However, the White House said that had no bearing on his visa application. The US has never denied a visa to a head of state to attend the UN general assembly, but did once refuse entry to Yassir Arafat, the Palestinian leader.

The US is pressing the UN to impose sanctions on Iran following its refusal to halt uranium enrichment by last week's UN-imposed deadline. China and Russia appear reluctant to move quickly with punitive measures, however, and this year's general assembly is likely to see intense lobbying by all sides.

Mr Ahmadi-Nejad told a cabinet meeting yesterday that the UN visit was a "good chance" for the debate and that the US side, if it wished, could bring advisers, according to his website.

On Tuesday Mr Bush launched a fierce personal attack on Mr Ahmadi-Nejad in a speech that equated what the US president called Shia Muslim extremists in Iran, Iraq and Lebanon (Hizbollah) with the threats presented by Sunni extremists affiliated to the al-Qaeda network. Iran and Iraq both have Shia majorities.

"We will not bow down to tyrants, and the world's free nations will not allow Iran to develop a nuclear weapon," Mr Bush said, referring to the Iranian president.

Mr Bush first called Iran part of the "axis of evil" in 2002. Iranian leaders habitually refer to the US as the "Great Satan".