Local residents said Persian-language television channels from the United States had been broadcasting callers throughout the day who had exhorted Iranians to turn out for demonstrations.
Two hundred riot police were drafted into central Tehran earlier in the day when more than 2,000 people started milling round the streets after a minor protest inspired by the U.S.-based channels, witnesses said.
“There have been callers from all over the place, even from places like Montreal, telling people to go out onto the streets,” said one with access to satellite television.
Spontaneous protests demanding greater social freedoms are rare in the Islamic Republic.
A Reuters witness saw dozens of cars near Valiasr Avenue, the tree-lined street that cuts the city north to south, repeatedly honking their horns. Another witness on a footbridge further down Valiasr saw more than 300 cars.
A group of volunteer militiamen arrived on motorbikes but there was no sign of any fighting. Hardline vigilantes crushed demonstrations by student activists last summer.
Eyewitnesses saw a further 300 cars driving up and down Jordan Boulevard, a boutique-lined street popular with the young and wealthy. The occupants made victory signs through the windows and blared their horns.
Earlier in the day, motorists tooted horns in support of what they perceived as a demonstration. A witness said scores of people had been chanting “freedom,” clapping and handing out pastries.
He said police had used their batons to push people from the scene but added there had been no fighting.
The ILNA labor news agency labeled the protesters monarchists, loyal to the shah toppled in the 1979 Islamic revolution.
Some of the crowd said they had turned out because of a call by the mystic Ahura Pirouz Khalegi Yazdi, who has predicted the fall of Iran’s government on Oct. 1. He broadcasts on a California-based channel and promised to charter aircraft to bring home the Iranian diaspora from the United States.
