The BBC's Jon Leyne reports live from Tehran
Iran's Guardian Council says it is ready to recount disputed votes from Friday's presidential poll, which has led to three days of unrest on the streets of Tehran.
The BBC's Jon Leyne in Tehran explains the fast-moving developments.
What does the Guardian Council decision mean?
It is once again a day here of fast-moving developments. The Guardian Council has announced that it is prepared to have a full recount of the votes, which is a massive U-turn over this election result.
However, I understand the opposition may not be willing to accept this. They believe that millions of ballot papers have gone astray, and therefore could not be counted. And they are still calling for a complete re-run of the election.
Defeated candidate Mir Hossein Mousavi did say he wanted demonstrations to be calm and peaceful. But if the opposition is refusing to accept the chance of a recount, won't that ratchet up the tension?
Demonstrations have re-started today, and there is even talk of a general strike. There is trouble at Tehran University. I have heard that 120 university lecturers there have resigned.
There are demonstrations planned for this afternoon, both by pro- and anti-Ahmadinejad supporters, and they are due to be in the same place.
I think the fear is that the government is trying to paint the opposition demonstrators as just a bunch of dangerous troublemakers - or "thugs" as they put it this morning.
How united or divided is the establishment today?
I get the impression that the establishment in Tehran is deeply divided. For example, the influential speaker of parliament, Ali Larijani - no softie himself - has in effect criticised President Ahmadinejad by condemning the Interior Ministry, which is loyal to him, for its part in a raid on student dormitories on Sunday night.
The demonstrations are now threatening the whole Islamic Republic. Its very survival is at risk.
So people must be worried. They must think they have fallen asleep and woken up again in 1979, because this is an eerie re-run of the events before the Islamic Revolution that brought them to power.
Who ultimately is calling the shots? Who is running this show?
You have still got to say that the country's supreme leader, Ayatollah Ali Khamenei, is the most important player. But I think there are people behind the scenes who must be pushing for some kind of resolution.
Mr Ahmadinejad is opposed by former president Akbar Hashemi Rafsanjani, a very influential figure who chairs two of the key bodies in this government, and the powerful parliamentary speaker Ali Larijani, who came out against the president, so the parliament is probably against this result.
So it is a house divided, and a house divided - as we know - cannot stand.
Is this not an extraordinary time for President Ahmadinejad to be taking a trip to Russia?
He has gone off to this regional summit meeting that is seen as being not so important for Iran. He made a bland statement to reporters about going off to discuss multi-lateral and bi-lateral issues. It is as if nothing at all were happening in Iran.