US Edition The threat of regime violence and the heavy police presence on the streets appeared to have deterred the vast majority of people who turned out in recent days to demand fresh elections.
The two main protest leaders, Mir-Hossein Mousavi and Mehdi Karroubi, who were beaten by Mahmoud Ahmadinejad in a disputed poll nine days ago, both called off official rallies.
Earlier in the day, the pair had been offered a minor concession when the Guardian Council, which supervises elections, promised to recount 10 per cent of the votes to check for election fraud - a suggestion that had previously been dismissed by protesters as a cyncial ploy to buy time.
As the confrontations began in the city centre, there were reports that a man had died in a bomb attack at the Ayatollah Khomeini shrine a few miles south of the city.
The blame seemed likely to rest on one of the ethnic separatist groups that have carried out periodic attacks in Iran over the past few years.
But it was equally likely that the incident would be seized upon by the authorities as evidence that election protests were being aided by terrorists.
Despite their smaller numbers, the crowd protesting yesterday were defying an explicit ban by Ayatollah Khamenei, the ultimate authority in the Islamic republic.
"I'm really tired and my feet are aching from all the walking last week but I have to go," said Rahil, a housewife who planned to attend yesterday's march. "This is an important day, I know there are risks but I don't have a choice."
In their first real show of force since massive street rallies erupted in central Tehran last week, the authorities deployed thousands of riot police and plainclothes Basij militiamen in the city centre.
Helicopters buzzed menacingly overhead.
As protesters began to gather near the university campus, chanting "death to the dictatorship", the police set upon them with baton charges, water canons and tear gas.
One demonstrator, who sought refuge in a house in the city centre, said she had heard gunshots, but did not know if live rounds had been fired.
In the hours leading up to the demonstrations, internet services were severely restricted and mobile phones were cut off in the centre of the capital.
Cordons of riot police, dressed in their military green uniforms with white stripes down the trouser legs and wearing heavy black helmets, stood in lines three deep along Enqelab (revolution) and Azadi (freedom) streets.
Together, the two roads form a long east-west highway bisecting the centre of the city and running past the main gates of Tehran University, a scene of turmoil throughout Iran's modern history.
It was along this street that millions of people surged to accompany Ayatollah Ruhollah Khomeini when he returned from exile to usher in Islamic rule in 1979.
According to a regular participant in last week's demonstrations, the protesters yesterday hoped to form large groups in side streets before bursting onto the main highway, thwarting attempts to disperse them.
Unconfirmed video footage posted online showed groups of people charging through the streets as teargas and smoke from a burning car swirled around them.
Riot police and men with sticks could be seen in the background.