Alireza, one of our Observers in Tehran, is currently in Shahrak-e Gharb, west of the city. He gave us this account at 7.30pm (10pm Tehran time), by phone:

The protesters have just started their rooftop demonstration and you can hear people shouting and chanting all around. They won't come down to the street at night because it's too dangerous.

Today's demo was different than pervious ones because the protestors have experience in facing the police now and they know how to avoid clashes. Instead of everyone walking together in the main streets they stay in small groups and take side streets. It's a new tactic that they've started today and it seems to have worked.

Because of that we don't know how many people came out. But one thing is for sure - while there might have been only a few thousand supporters, there were, and still are, up to 10,000 guards, Basij members and policemen. They are everywhere."

8pm: Clashes between security forces and demonstrators at Vali Asr Square, Tehran. Filmed at 8.30pm Tehran time.

7.42pm: Enghelab Avenue, Tehran, blocked by guards on motorbikes this afternoon.

7.12pm: Students on Tehran's Sharif University campus surrounded by guards.

6.48pm: First images of clashes. Filmed at Tehran University.

6.28pm: Alireza, one of Observers in Tehran, gave us this account:

There haven't been any serious protests in Tehran. Students have been gathering together in certain places in the city but there are so many police around that it's impossible to get a proper protest going."

6.12pm: The entrance to a road blocked off by police in the "College Bridge" district near Tehran University.

6.02pm: Protesters at Sharif University, Tehran.

5.15pm: More videos of protests at Sharif University (for example). Still not confirmed. The students are chanting "Mousavi, Mousavi", while the opposition leader called on supporters not to protest... The internet connection is very slow, but we're managing to talk to some of our Observers.

4.42pm: One of our sources in the capital says that teargas is being used on Enghelab Avenue. Protester numbers remain unknown.

4.01pm: It seems that the video taken at Sharif University is not from today.

4pm: Police stationed in front of Tehran University. Students shouting slogans.

3.59pm: Clashes on Enghelab Avenue confirmed.

3.32pm: SMS messages blocked across the country. We can no longer get hold of our Observers by Internet. The Internet seems to be completely blocked.

2.50pm: Clashes outside Tehran University. Basij militia members storm the grounds.

2.15pm: Two of our Observers say that people are gathering on Enghelab Avenue.

12pm (Paris time): Police deployed to Tehran streets.