By Sadeq Saba
BBC regional analyst
A call from a US-based Iranian TV personality has prompted thousands of Iranians to protest for more freedoms.
Iranians are showing signs of desperation for change
People took to the streets of the capital, Tehran, and other cities on Sunday after Ahura Pirouz Khaleghi Yazdi urged protests across Iran.
The exile has predicted Iran's Islamic government will fall on 1 October.
Nobody had heard of Mr Yazdi until a few months ago when he set up a satellite channel in California to try to overthrow the Iranian government.
Since then he has become a hot topic of conversation both among disaffected Iranians and exiled opposition groups.
For several weeks he has been declaring that he intends to return to Iran on 1 October to end the rule of Islamic clerics.
He has called on the Iranian diaspora to accompany him in his so-called liberation flight and has urged his supporters inside the country to stage protests.
He is advocating peaceful means and civil disobedience.
Mr Yazdi, who seems to be about 50, apparently left Iran when he was a child - and his command of the Persian language is poor.
The pro-government press in Tehran has described him as insane.
His simplistic views about overthrowing the Islamic government singlehandedly have also angered serious exile opposition leaders who have labelled him a demagogue.
But analysts say the fact that thousands of people heeded his call and took to the streets on Sunday evening proves that Iranians are desperate for change.
The Yazdi phenomenon also shows how US-based opposition satellite TV stations are becoming an important means of putting pressure on the Iranian government.