The softly-spoken former leader will become the most senior Iranian figure to visit America in nearly three decades. He is expected to attend the United Nations “Dialogue of Civilisations” conference in New York on September 5, address an inter-faith meeting at the National Cathedral in Washington on September 7 and give a speech to an Islamic group in Chicago.

The highlight could be a meeting with Jimmy Carter, the former US President, who heads the Carter Centre in Atlanta, a conflict-resolution organisation.

Iranian and American officials insist that the visit by Mr Khatami and his entourage of aides and family members is purely private. No meetings are planned with members of the Bush Administration and he will not be representing President Ahmadinejad, his hardline successor.

But experts on the region are hopeful that the visit could open a channel between America and Iran, who have no diplomatic ties and whose dialogue is usually confined to public threats and insults.

“This is an important visit because Khatami does still have clout in Iran,” said Dr Ali Ansari, an expert on Iran at the University of St Andrews. “Much will depend on how the visit is handled. It is a very delicate matter.”

Certainly, the former Iranian leader who tried to improve ties with the West during his tenure from 1997 to 2005, will have his work cut out. His trip to America coincides with the expiry tomorrow of a UN Security Council deadline on Iran to halt its uranium enrichment work, which it is alleged could be diverted to produce a nuclear weapon.

The Iranians have already said that they will not halt the programme and a report to be presented to the Council by Mohammad ElBaradei, the head of the International Atomic Energy Agency, is likely to accuse Iran of accelerating the enrichment work.

America, Britain and France want the Council to move ahead with punitive sanctions against Iran that would target key figures in the regime and ban the sale of nuclear equipment and possibly arms. China and Russia, the two other permanent members of the Council with strong commercial ties to Iran, favour a more diplomatic solution.

While the outlook appears stark, diplomats involved in negotiations with Iran are convinced that a deal is still possible between Washington and Tehran that could settle all outstanding issues stretching back to the Iranian revolution in 1979 which swept the Islamic regime into power.

By a twist of fate a key figure in mediation efforts could be Mr Carter, the former US president. He lost his re-election bid in 1980 in part because of the Iranian hostage crisis, when militant students seized 52 American diplomats and held them for 444 days. Since then he has dedicated his career to conflict resolution and now stands ready to meet Mr Khatami.

But the visiting Iranian leader will not be welcomed everywhere he goes in America.

The Simon Wiesenthal Centre has launched a petition calling on the Bush Administration to block the visit.

“Granting former President Khatami a visa at this time, coming on the heels of both Iran’s proxy war in Lebanon and its refusal to drop its nuclearisation program, will be viewed by the mullahs as a reward for their policy of confrontation and hatred toward the United States and her allies,” the organisation said.

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