7.30am

The Iranian opposition movement has been debating new dates to renew their street protests since they last took to the streets in significant numbers on Qods day in September. They opted for today in attempt to hijack another official rally. It's Students Day when Iran celebrates the 1979 takeover of the US embassy in Tehran with anti-US demonstrations.

Here's some of the background:

• The defeated opposition candidates Mir Hossein Mousavi and Mehdi Karoubi have urged their supporters to take to the streets.

• Official anti-US rallies are planned to take place outside the US embassy.

• Tehran's police force has warned it will "strongly confront" any other gatherings.

• Rumours have been flying about what may happen today. There's speculation that pro-regime students plan to storm the UK embassy, but there's also talk that opposition protesters may do the same to the Russian embassy.

There continues to be tough restrictions on journalists in Iran which means that reliable information is difficult to obtain, so if you are in Iran and have news, please email me at matthew.weaver@guardian.co.uk or post updates or useful links in the comments section below.

7.35am:

Police fired teargas to disperse thousands of protesters, a witness told Reuters.

Usually reliable sources on Twitter said there has been a repeated use of teargas in Hafte Tir Square in Tehran. They also report that some protesters have been violently beaten by the security forces wielding batons. Metro stations have been blocked and there's a heavy police presence.

7.57am:

Unsurprisingly the state media is ignoring the opposition protests and focusing instead on the official anti-US rallies. Press TV claims: "Tens of thousands of people from all walks of life and many political persuasions have staged a rally at the site of the former US embassy in Tehran, better known in Iranian history as the 'den of spies'."

8.01am:

Five protesters have been arrested, according to Reuters. It also gives more details of clashes and the movements of the security forces outside both the US and Russian embassies.

8.06am:

One of opposition leaders Mehdi Karoubi has been seen in Hafte Tir Square, according to ABC reporter Lara Setrakian, citing a colleague.

Callers to the dissident Iranian radio station ePersian radio also report seeing Karoubi among the protesters, according to translations from blogger Homylafayette.

The website of ePersian radio seems to be overloaded, but you can listen in here.

8.33am:

The usually trustworthy opposition website Mowjcamp claims shots have been fired in Hafte Tir Square and that protesters have been injured, according to a translation from Saeed Kamali Dehghan, who is in London after reporting from Tehran.

8.39am:

Police are wearing teargas masks for the first time, according to an email from a contact in Tehran. He also reports that the security forces are filming protesters and that most of the government buildings in central Tehran are closed.

8.45am:

The first videos claiming to show today's protests are starting to appear on YouTube. This one is appears to have been shot undercover so it is difficult to get a sense of what is going on, but the crowd can be heard chanting "don't be afraid, we are altogether" and "down with the dictator". Fires can also be seen burning in the streets - a sign that teargas has been used as the smoke weakens the power of the gas.

9.04am:

Once again news of the protests in Tehran is spreading rapidly on Twitter as Trendsmap demonstrates.

One of the biggest trending topics is #13aban, today's date in the Iranian calender.

9.10am:

Shouts of "down with the dictator" were clearly audible on state TV during live coverage of a speech by the hardliner Haddad Adel at the official ceremony, according to a 12.15pm (local time) update from the blogger Revolutionary Road.

9.15am:

Protesters can be seen fleeing a baton charge in this video, apparently taken today from Karimkhan bridge in central Tehran. (You have to tilt your head to watch it.)

9.23am:

Today anti-regime protests are not confined to Tehran. There have been reports of thousands gathering in the southern city of Shiraz and Isfahan in central Iran, and in this video shows a small opposition rally in the northern city of Rasht.

9.28am:

A contact emailed the Guardian from Tehran to report more clashes in Ghaem Magham Farahani street near Hafte Tir Square. Some were covered in blood after being shot at, the witness said

He also confirmed that rubbish has been set on fire in the street to help combat teargas.

9.32am:

The Guardian's middle east editor Ian Black has filed a backgrounder on today's protests which is due to be published soon. Here's a preview:

Iran-watchers and analysts at home and abroad say today's "nest of spies" events could be a test of how hard the regime is prepared to crack down again after a period of relative calm in recent weeks — and perhaps provide some clues about apparent disagreements between hardliners and more pragmatic elements. Another point to watch is the coherence of the Greens' leadership: what is the role of Mehdi Karoubi, another defeated reformist candidate, and of Mohammed Khatami, the former president who Ahmadinejad defeated in 2005?

9.39am:

Karoubi has been roughed up by "agitators," according to the reformist website Mowjcamp. His bodyguard helped him leave the scene, it says.

There has been little word so far about Mousavi.

9.42am:

"Russian Embassy - nest of spies", chant the protesters in this clip in a twist to the official anti-US slogan.

9.51am:

A friend of a usually reliable source on Twitter has been hit in the eye by a plastic bullet and has been take to hospital.

9.56am:

This video gives a better idea of the scale of today's protests. The protesters are singing a popular Iranian song that has been chanted several times in the past month in protests held in the universities, according to my colleague Saeed.

10.01am:

Two bus loads carrying around 50 arrested protesters has been seen near Shahid Shiroudi sport complex in Tehran, according to an update on the opposition forum Balatarin.com.

The Guardian's database of those killed and detained in the protests is still being updated.

10.12am:

Around 200 protesters gathered outside the headquarters of the official news agency IRNA, it reported.

Opposition websites suggest that more people were involved.

Striking photos of protests elsewhere have been uploaded to Twitpic.

10.17am:

Riot police are seen violently attacking protesters in this video after about two minutes of chanting. Protesters were shouting slogans in praise of Karoubi and Mousavi and were calling for political prisoners to be released.

10.27am:

Security forces mainly paramilitary units from the Revolutionary Guard swept through an opposition march in central Tehran, clubbing some protesters and kicking and slapping others, according to Associated Press witnesses.

10.32am:

Twenty people have been arrested and several injured in the southern city of Shiraz following clashes between protesters and the security forces, according to the reformist website Rahesabz, writes our former Tehran correspondent Robert Tait.

The report also said police had fired more than 100 shots in the air to disperse demonstrators. Agents in plain clothes have been filming and photographing the scene. Shiraz, a city for its Persian poets and relaxed atmosphere, was the scene of particularly violent clashes in the immediate aftermath of June's disputed election.

10.39am:

New video purports to show protesters dressing bleeding head wounds after clashes with the security forces.

Similar scenes can be seen on Twitpic.

10.47am:

Karoubi's son claimed teargas was directed at his father. In an interview with Radio Farda Mohammad Taghi Karoubi, said: "The official forces directly targeted Mehdi Karoubi and fired teargas toward him."

Video shot earlier shows Karoubi on his way to the demonstration. Another video shows a closer view of him being mobbed by supporters.

10.51am:

Barack Obama has issued a statement on Iran. He said:

We have heard for thirty years what the Iranian government is against; the question, now, is what kind of future it is for. The American people have great respect for the people of Iran and their rich history. The world continues to bear witness to their powerful calls for justice, and their courageous pursuit of universal rights. It is time for the Iranian government to decide whether it wants to focus on the past, or whether it will make the choices that will open the door to greater opportunity, prosperity, and justice for its people.

In this video protesters chant "Obama, are you with us or against us?"

10.54am:

Criticising the supreme leader Ayatollah Khamenei used to be taboo. Now protesters are accusing him of being a "murderer". In this video they also shout "his leadership is over". It was apparently taken today in Keshavarz, central Tehran.

11.14am:

Habiballah Peyman, a senior member of the opposition National Religious Party, has been badly beaten, writes Robert Tait, citing a report on the reformist website Mowjcamp.



He was left with a fractured skull after being attacked by pro-regime vigilantes, who assaulted him with batons and also smashed his glasses. His wife was also hurt in the incident, which apparently happened in the main demonstration commemorating the embassy takeover. Peyman is an outspoken character and has previously spent time in prison for his views.

11.23am:

There are unconfirmed reports, repeated by the Times, that those arrested include the mother of Neda Soltan, the student whose shooting in June made her an icon of the protests.

11.27am:

Soltan, a photo-journalist contact in Tehran, took this picture of today's protest .

11.56am:

Here's another picture from Soltan.

12.04pm:

This would be the biggest opposition demonstration since the rallies in June if the reports of the unrest are correct, the broadcaster al Jazeera claimed.

12.23pm:

A 60-year-old woman returned from the demonstrations to describe the violent crackdown in a call to ePersian radio, according to this translation from blogger Homylafayette.

I joined the demonstration early today and moved towards 7th Tir Square. There were so many protesters. They must have bought security forces from around Iran and they were merciless. I've gone to all the demonstrations and I've never seen such violence. We started chanting and they chased us down a dead end. We were all crushed together and the anti-riot forces shot something like 5 tear gas canisters into the alley. I thought my time was over and I would suffocate. Then the anti-riot forces came into the alley started beating us with their batons. I was hit on the waist and the mouth. Protesters were all over the city today. They would get beaten in one place, then they'd go to another crossroads and start chanting again. This regime must go! It pained me to see the young people struck like that. I'm going to rest, then I'll go out again, because the protests are going to pick up again.

12.36pm:

Another video from outside Tehran appears to confirm that the protest are not confined to the capital. It shows protesters chanting "down with the dictator" in the southern city of Shiraz.

12.39pm:

School children have also joined protests shouting "Death to the dictator", according to the opposition website Mowjcamp.

Witnesses said student were wearing green on their way to schools. There are also unconfirmed reports that pupils have been writing in green ink today.

Teargas was thrown into a Dr Hesabi school in Tehran, according to an unconfirmed report.

In the run up to today's protest pupils in Imam Reza School in Mashhad voted for Mousavi in school council elections.

And in Kashan, in central Iran, 235 schools were temporarily closed officially to combat swine flu. The opposition see it as way of trying to clamp down on potential protests as there have been few cases of the disease in the region.

12.56pm:

Basij forces carrying batons can be seen in a new collection of photos from today from the dissident news agency Gooya.

1.03pm:

At the official rally pro-regime supporters have been burning US flags and trampling on them, but opposition protesters have stamping on images of Ayatollah Khamenei.

1.37pm:

The reason we haven't heard much about Mousavi is that he's been barred from leaving his house by the security forces, according to the Czech-based broadcaster Radio Farda.

Mousavi's official website confirms that he was prevented from joining the demonstration.

1.42pm:

Basij forces are shown beating protesters in Tehran in this video purportedly taken today.

1.56pm:

US and Israeli flags are seen burning in the images of official student's day protest, published by Fars news. Like the images and film of the protests it is difficult to verify when they were taken.

2.20pm:

"Obviously this was a well planned effort by the government to handle the protests," reports a correspondent for Tehran Bureau who said the demonstrations were much smaller than those in the summer.

The writer adds:



I got to Karim Khan bridge and saw a large group of police amassed in riot gear. Many green-clad people were moving West, away from Hafte Tir Square, but they were not amassed like the demonstrations in June. Instead, they moved along the sidewalks. I saw less violence than before, and though I did see the usual old basiji acting as self-appointed police wherever they were, most of them were just pissed off and yelled back at the protesters.

2.31pm:

The BBC Persian service has published a new collection of photos from today's protests.

2.34pm:

Thousands of protesters are shown here at the crossroads of Valiasr Street and Motahari Street, in Tehran. Some can be heard chanting "no east, no west, a national green government". They also chant that Ayatollah Khamenei is a killer.

In this one they chant that a green Iran doesn't need nuclear weapons.

2.52pm:

The citizen photo-journalism website Demotix has published a fresh collection of images from today including a picture of what looks like a protester kicking away a smoking teargas shell.

3.11pm:

"Down with English" said the placard carried by one participant in the official rally. It is featured in a gallery of more than 30 images from the website of the Turkish newspaper Hurriyet. Most show the official rally, but there are striking images of the protesters too.

3.20pm:

Protesters are shown tearing down an official billboard image of Khamenei at the end of this video.

The same YouTube user has also uploaded footage that purports to show protesters being arrested today.

(That's it from us today, thanks for your comments.)