By Jon Leyne
BBC News, Tehran
The opposition is said to be trying to become more organised
The crisis over the Iranian election has developed with such dizzying speed it is hard to take in the implications.
Until barely two weeks ago, anti-government demonstrations were unheard of.
Now the opposition routinely turns out hundreds of thousands of protesters on the street every day.
Last weekend, President Mahmoud Ahmadinejad could claim that Iran was "almost completely free".
There were sceptics at the time.
Now the foreign media are operating under some of the most sweeping restrictions in the world.
So where is this crisis going, and what do the opposition want?
'Not open challenge'
For the moment, the demonstrators have just one demand - a re-run of the election they believe was won by the opposition leader Mir Hossein Mousavi.
Ayatollah Khamenei has publicly supported President Ahmadinejad
When they chant "death to the dictator", they do not say who they mean. But the suspicion is they mean not just President Ahmadinejad, but also the Supreme Leader, Ayatollah Ali Khamenei.
Nevertheless, this is not an open challenge to the system, at least not yet.
The women in the demonstrations do not take off their headscarves, for example, even though many detest being forced to wear them.
And the demonstrators chant "God is Great" to stress that they are just as religious as supporters of the government.
The government acts with a display of wounded dignity.
The very idea that they have rigged the election is unthinkable, they suggest, even though the opposition believe the fraud was quite blatant.
Foreign ambassadors are called in, one after the other, and given a dressing down for even daring to criticise the shooting of demonstrators.
Meanwhile, the authorities have been sending out their thugs, the "Basijis" - members of the government militia - in a blatant display of intimidation.
Student dormitories are ransacked. Protesters are picked off on the edge of demonstrations. Apartment blocks where Iranians are chanting on the roof are broken into, and cars trashed.
And widespread arrests have now stretched as far up - to include the man who was one of the closest aides of Ayatollah Khomeini, Ebrahim Yazdi.
So far there has been no decision taken for a really sweeping crackdown, though that may come sooner rather than later.
Meanwhile, a separate power play is going on at the top of the political system.
Former President Rafsanjani is backing the opposition
Ayatollah Khamenei has staked his political life on his unequivocal support for President Ahmadinejad's re-election victory.
He has many cards in his hand. He is the supreme commander of the armed forces. He is also loyally supported by the Guardian Council, which is reviewing the election result. Until now , no-one ever dared question his authority - at least openly.
But on the other side is former President Akbar Hashemi Rafsanjani, who has been backing the opposition campaigns.
As the election began, it became clear he wanted revenge against President Ahmadinejad, who beat him in the presidential election four years ago.
And there is probably a deeper rivalry with the supreme leader himself, whom Mr Rafsanjani helped to power when he succeeded Ayatollah Khomeini in 1989.
The rivalry really erupted when President Ahmadinejad accused Mr Rafsanjani's family of corruption during one of the televised presidential debates.
They may be arguing over a disputed election. But they are really arguing over the future of the country. A momentous, titanic struggle, whose outcome no-one can predict
It is an accusation many Iranians might suspect is true, but the manner in which it was made caused outrage.
Mr Rafsanjani wrote an unprecedented letter to the supreme leader, calling him to act, and issuing a remarkable threat.
If nothing was done, "the volcanos fed inside burning chests will appear in society, as exemplified by gatherings we have seen in streets, squares and universities".
The flames, Mr Rafsanjani warned, would spread "through the elections and beyond".
Mr Rafsanjani has some powerful tools.
He heads the Assembly of Experts, the body of clerics in charge of electing, supervising and dismissing the supreme leader.
For them to take action would indeed be unprecedented. But Mr Rafsanjani recently won re-election with a big majority. And Ayatollah Khamenei has many enemies amongst the clerical establishment.
Mr Rafsanjani also heads the Expediency Council, which mediates on disputes between other organs of government. Not to mention his almost legendary wealth.
Do not underestimate the fervour of supporters on both sides.
There may be government supporters encouraged or bussed to demonstrations, but there are many who also genuinely adore Mr Ahmadinejad.
And for the opposition, the disputed election has unleashed years of frustration over a system that prevents them from meeting their aspirations.
They may be arguing over a disputed election. But they are really arguing over the future of the country. A momentous, titanic struggle, whose outcome no-one can predict.