Mir Hossein Mousavi has unleashed a vehement denunciation of the result, in which he has challenged the authority of Iran’s supreme leader, Ayatollah Ali Khamenei.
It is a brave move given that Iran’s Basij militia today called for an investigation of Mousavi, accusing him of “disturbing national security”, which is punishable by 10 years in jail.
On his website, Mousavi said President Mahmoud Ahmadinejad’s future government would be “illegitimate” and in another article, Mousavi wryly observes the deafening silence from senior Shia clerics who have not condemned his challenge to Khamenei. It is because they cannot lie before God, he suggests.
Mass protests have died down, but new, undated pictures are still being posted on the web. It is believed that across the country thousands may now have been arrested by riot police, Revolutionary guards and Basij paramilitaries.
Mr Mousavi today demanded the release of detainees that he called “the children of the Revolution”, language pointedly suggesting a betrayal of the ideals of the Islamic Revolution.
In New York, international human rights groups claimed political prisoners in Iran were being forced to make false confessions.
Iran accuses foreign powers, particularly Britain and the United States, of attempting to orchestrate another “colour revolution”.
The row over the detention of locally employed British embassy staff rumbles on, although it has now been reported that all but one of the nine originally arrested have now been freed.
An Iranian news agency had earlier said one of the embassy staff had played “a remarkable role during recent unrest, managing it behind the scenes”. The British government calls the allegations “unfounded”.