Iran´s foreign minister called for "comprehensive, long term dialogue" yesterday as the adversaries in the confrontation over Tehran´s nuclear ambitions prepared for crucial talks.

The negotiations set to open in Istanbul on Saturday will be the first time that Iran has formally met the world´s leading powers for more than a year. Unlike during a previous round of fruitless talks, Tehran has agreed to discuss its nuclear programme without preconditions.

Ali Akbar Salehi, the foreign minister and a relative moderate in Tehran´s opaque power structure, sounded a conciliatory note yesterday, saying: "We hope that all sides will return to the negotiating table as equals with mutual respect; that all sides will be committed to comprehensive, long-term dialogue."

Writing in the Washington Post, Mr Salehi added that it was "most important that all sides make genuine efforts to re-establish confidence and trust".

However, the gap between the two sides remains immense. Iran insists on its right to enrich uranium, a highly sensitive process that could be used to make the essential material for a nuclear weapon – although Mr Salehi adamantly denied any such intention.

Meanwhile, the six world powers who will meet Iran´s representatives today want Tehran to obey six United Nations resolutions and stop all enrichment. This group consists of the five permanent members of the Security Council – Britain, America, France, Russia and China – along with Germany.

But they are also riven by divisions, with Russia and China taking a markedly different line towards Iran than the Western members of the group.

Nonetheless, experts said that today´s talks could succeed in at least lowering the temperature of the confrontation.

"I´m cautiously optimistic, because I sense the main goal for these first talks may be sensibly modest: just to get a process launched," said Peter Jenkins, who negotiated with Iran as Britain´s ambassador to the International Atomic Energy Agency between 2001 and 2006. "I think it would be a mistake for the West to go in with extravagant demands that might precipitate another breakdown on the very first lap."

But American officials have laid out clear demands: they want Iran to close the Fordow nuclear plant, a once secret facility constructed in breach of international safeguards. They are also likely to ask Iran to export the uranium it has already enriched to 20 per cent purity – a vital step towards the 90 per cent required for nuclear weapons.

Ben Rohdes, the US deputy national security adviser, yesterday called on Iran to show "seriousness" about moving forward with dialogue.

Iran´s representatives have already voiced their opposition to these demands. Mr Jenkins cautioned against expecting a swift result, even if today´s talks go well. "This issue will only ever be resolved via a protracted process. The complexity is such that it could not be otherwise," he said. (© Copyright of Telegraph Media Group Limited 2012. 04/14/12)