Seen as being most at stake is Iran's relatively pragmatic approach in diplomacy over its nuclear programme, which Iran maintains is for peaceful purposes but is seen by many as the cover for weapons development.

Ahmadinejad's rival for the presidency, Akbar Hashemi Rafsanjani, has been considered as the man in driving seat on the Iranian side -- sticking by a freeze of sensitive nuclear activities and talks with Britain, France and Germany.

"It is extremely important to understand that what is at stake is this process concerning dangerous nuclear materials," French Foreign Minister Philippe Douste-Blazy cautioned after Ahmadinejad was thrust into a shock run-off against Rafsanjani.

"In the past, Mr Rafsanjani has had a slightly more liberal attitude and we have felt in the last several weeks that there has been an easing of tensions between Iran, the European Union and the international community on this subject."

Rafsanjani, an ex-president and savvy deal-maker, has also spoken of the need to "solve" a quarter of a century of estrangement with the United States.

But a loss by the regime veteran could see both him and Iran's nuclear negotiators, including Rafsanjani loyalists such as Hassan Rowhani, squeezed out amid a wider political shift to the right.

According to Ahmadinejad, currently Tehran's mayor, "those who are handling the talks are terrified, and before they even sit down at the negotiating table they retreat 500 kilometres."

"A popular and fundamentalist government," he added, "will quickly change that."

An Ahmadinejad win would also place every Iranian elected and non-elected institution under the control of Iran's anti-Western religious right, ending what has up to now been a delicate equilibrium in decision making between moderates and hardliners.

While the president is only Iran's number-two on paper -- and often lower than that in practice -- Ahmadinejad would bolster the ranks of right-wingers who argue Iran has a "legitimate right" to press on with nuclear work and, more importantly, should do so regardless of the consequences.

At the core of the issue is Iran's ambition to make its own nuclear fuel by enriching uranium, a process that can also be used to make the core of a nuclear bomb.

"It's impossible to stop a nation's scientific progress with a bunch of irrelevant words," Ahmadinejad said in a campaign statement, describing Iran's atomic ambitions as "a flood which cannot be stopped by a match stick".

"We will hold talks from a rational point of view and if they accept our legitimate right we'll cooperate," the statement, warning that Iran will not accept lengthy talks and "the kind of games they have played with Palestinians".

"The analysts say no country, no matter how powerful they are, can attack Iran. It would be suicidal for a country to attack Iran... so we must not bend to threats," he argued.

Indeed, for Ahmadinejad, it should be Iran that calls the shots in the talks.

"We spend 30 billion dollars on imports, and this is an immense means of pressure in negotiations. It is us who should impose our conditions on them and not them on us, and if they do not accept our conditions, it's simple -- we won't buy anything from them," he said in a campaign broadcast.

Any easing of tensions with Washington would also be off the cards.

"The US administration cut off ties unilaterally to lay waste to the Islamic republic," he argued. "They want to restore them today for the same reason."

Diplomats close to the EU-Iran nuclear talks can only watch and wait.

"We're holding our breath," one told AFP. "It does not mean Rafsanjani will be easy to negotiate with, but at least we know he is more or less committed to the negotiating process. If Ahmadinejad is elected, it will be very uncertain what will happen."

"In any case, our position will stay the same," said another diplomat. "If Iran decides to break its nuclear commitments, we are going to theSecurity Council."

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