President Ahmadinejad is facing pressure at home and abroad
By Roger Hardy
BBC Middle East analyst
Weakened by months of dissent over June's disputed elections, the ruling clerics in Tehran want to distract attention from their domestic problems - and show leadership on an issue of national importance.
On 1 October, Iran will discuss the nuclear issue in Geneva with the five permanent members of the UN Security Council (the US, Russia, China, Britain and France) plus Germany.
Few observers expect the "five-plus-one" talks to make much headway. Mistrust is the order of the day.
But Iran has its own reasons for showing up - and playing for time.
Among Iranians, the nuclear issue commands a broad national consensus.
To possess the same capability as Israel - not to speak of India and Pakistan - is viewed as a matter of national pride.
It's a view opposition leaders share.
The opposition dislike President Ahmadinejad and are well aware he is manipulating the nuclear issue for his own ends.
But their hands are tied. They have no wish to appear unpatriotic on the issue - or unduly sympathetic to Iran's foreign critics.
The main opposition figures - Mir Hossein Mousavi, Mehdi Karroubi, Mohammed Khatami - all support Iran's nuclear ambitions. So does former president Hashemi Rafsanjani, regarded as sympathetic to some of the opposition's grievances.
Similarly, they are against tougher international sanctions - which the Americans and the Europeans want to introduce if the Geneva talks go nowhere.
The regime knows this, and wants to exploit it, to regain abroad the legitimacy it lacks at home.
By starting a dialogue with the West, it hopes to ease the intense international pressure it's under.
To this end, it is ready to make tactical concessions - but without compromising on what it regards as its inalienable right to enrich uranium.
That is a red line it is unwilling to cross.
It hopes that by engaging in dialogue, it will enable its friends in Russia and China to block the "crippling" sanctions which the Americans are threatening to impose.
So the "five-plus-one" face a dilemma.
They agree that dialogue is worth a try. But to make concessions to Iran would be seen as rewarding a regime widely seen as illegitimate - and strengthening its hand vis-a-vis the opposition.
The alternative - breaking off talks and going for tougher sanctions - offers no guarantee of success either.
According to the New York Times, President Ahmadinejad told guests at a dinner in New York last week that he would "warmly welcome" additional sanctions because it would make his country more self-sufficient.
That might sound like bravado.
But this is a regime that has shown it will absorb punishment in the interests of pursuing a cherished ambition.
Despite Iran's internal turmoil, the essentials of the nuclear conundrum remain stubbornly unchanged.