A BBC correspondent describes Iran's capital in the aftermath of a massive security operation to prevent opposition protests over disputed election results.
Small groups of demonstrators held running battles with police
Security forces were everywhere in central Tehran in the late afternoon and early evening.
As I spent a couple of hours driving around in heavy traffic I could see thousands of men, some uniformed members of the military riot squads, some units of revolutionary guard, and everywhere basijis - militiamen who look like street toughs.
The security men were deployed on every street corner, in long lines down the sides of the roads, and in all the main squares.
The basijis wore riot helmets and carried big clubs. It was designed to intimidate, and while I was there, it was working.
There were hundreds in Enghelab [Revolution] Square, close to Tehran university. Traffic was being allowed to use it, with the drivers being eyeballed by the men with clubs who lounged in thick groups wherever you looked.
All this was happening against the background of a city open for business, where commercial life was going on.
Shops this evening were not shuttered. The streets were jammed with cars, with mopeds and motorbikes buzzing around them.
The pavements were full too. Some of the people looked as if they were waiting for some leadership, for a demonstration that they could join.
From time to time small groups would come together and try to move down the street together chanting and clapping.
I saw one group of demonstrators, perhaps 400-500 people, walking briskly down one side of a major road in the city centre. Bystanders were waving and making gestures of support.
Then, very quickly, tear gas canisters were fired into the crowd, and they broke and ran. It was a hot, windless evening, and the gas hung over the streets, prickling noses and eyes long after the demonstrators were dispersed.
In places you could see the evidence of where trouble had been - smashed glass in a bus stop, an overturned rubbish skip. And at different places and times, roads were closed while the security forces dealt with the people that were there.
Iran's Supreme Leader had issued a stern warning at Friday prayers, warning opposition leaders that they would be responsible for "bloodshed and chaos" if the protests continued.
No doubt firearms were not far away this evening, but I did not see any security men armed with anything more than clubs and tear gas launchers.
The government forces might have wanted to scare people off the streets without using the violence of which no one here doubts they are capable.
They may have chalked the day up to them. But putting security men on the streets does nothing to deal with the fundamentals of this crisis.
The Islamic republic of Iran continues to move into unknown territory. No-one knows where this will end.