Mohammad Khatami says millions have lost faith in the electoral process
The former President of Iran, Mohammad Khatami, has called for a referendum on the legitimacy of the government, following June's disputed elections.
Mr Khatami, quoted on Iranian websites, said millions of Iranians had lost faith in the electoral process.
The Iranian opposition, including Mr Khatami and the defeated presidential candidate Mir Hossein Mousavi, say the election was rigged.
Only the Supreme Leader, Ayatollah Ali Khamenei, can organise a referendum.
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I wanted Rafsanjani to ridicule Ahmadinejad directly, after all Ahmadinejad insulted Rafsanjani and his family
Armenian, Tehran, Iran
Ayatollah Khamenei has already declared the elections, which the incumbent, President Mahmoud Ahmadinejad, won by a landslide, as valid.
Thousands of opposition supporters took to the streets after the poll results were announced, to protest against what they saw as mass fraud. At least 20 people are believed to have died in the clashes.
There were more public protests last Friday after a sermon by another important pro-reform figure, former president Ali Akbar Hashemi Rafsanjani.
Mr Mousavi has continued to issue statements opposing the election result, saying detention of protesters would not end opposition.
"Isn't it an insult to 40 million voters... linking detainees to foreign countries? Let people freely express their protests and ideas," Mr Mousavi said on his Ghalamnews website.
Mr Khatami said there was no alternative to having a referendum, which he called for an independent body to carry out.
"I state openly that reliance upon the people's vote and the staging of a legal referendum is the only way for the system to emerge from the current crisis," Mr Khatami said.
"People must be asked whether they are happy with the situation that has taken shape," he said.
He suggested that an impartial body such as the Expediency Council should hold the referendum and pledged that his political supporters would respect the result whatever it was.
He also praised the sermon on Friday, by former president and current Expediency Council head Mr Rafsanjani, who said the government had lost the trust of millions in Iran.
In the sermon at Tehran University, Mr Rafsanjani also called for all those detained since the elections to be released.
His words - broadcast live on state radio - brought thousands back out onto the streets, the first public opposition demonstration for more than a week. They chanted slogans in support of Mr Mousavi.
Police fired tear gas to break up crowds and witnesses said there were a number of arrests.