2050 GMT: Deutsche Welle carries this account from a participant in the protest in Tehran (translation by Tehran Bureau):
The number of security forces today in Tehran was higher than February 14 and 20. There were a lot of plainclothesmen. The security forces hit the protesters hard in an attack at Vali Asr Crossroads and closed off the area. They fired a few shots in the air and the crowd dispersed.We waited for half an hour in one of the side streets of Vali Asr and then exited with a few others. In the dark and cold, we started walking toward Enghelab and Azadi Squares. The entire crowd were walking toward the west on the sidewalks, but there were a lot of plainclothesmen among the people....Every now and then, security forces would politely take someone aside and check their camera, cell phone, bag, or wallet and then take a picture. I could see people on scaffolds, taking people's pictures from a wide angle after a minute's pause.
Right before Navab Avenue, the crowd got denser and security forces moved to disperse them. People quickly turned down side streets. Some said there were clashes on Navab and they don't want people to get there. We went toward Tohid like the other times. Then, we went toward Azadi and saw that people were moving away from the avenue because there were clashes down there. People were being attacked by security forces and plainclothesmen....
Security forces had brutally attacked protesters. Some people told us they had fired shots in the air repeatedly.
I can't say how many people were there. But I can tell you that half the people on the sidewalks were security forces and Basij.
2030 GMT: Promising Justice. The Iran Prosecutor General Gholam-Hossein Mohseni-Ejei has promised that the criminal case involving Saeed Mortazavi, the former Tehran Prosecutor and current Presidential aide, will be strictly reviewed.
Mortazavi is accused of involvement in the post-election abuses that killed at least three detainees in Kahrizak Prison. He was technically dismissed from his post by the Tehran Military Court but has retained duties as an advisor to President Ahmadinejad.
Senior clerics and politicians, as well as the families of political prisoners and opposition figures, have called for Mortazavi's prosecution.
2002 GMT: A report from Banooye Sabz on Tehran, posted about 90 minutes ago:
People moving from Keshavarz Street to Enghelab chanting "Death to Dictator" and "Allah O Akbar". Eye witnesses reporting that there is no mobile reception. Gatherings and clashes between Azadi and Enghelab Square. Motor cycle police are attacking people with batons on side walks. People keep moving towards Azadi square singing "Yareh Dabestanieh Man". On Eskandari street many young protesters were arrested and transferred onto buses.
2000 GMT: A poster alongside Niayesh Highway in Tehran "Dictator, Say Hello to the End"
1900GMT: This report from Tehran Bureau:
Saham News claims that protests continue in different parts of Tehran. Reports of chants of "Mousavi and Karroubi must be freed!" coming from the center of the city. BBC Persian's TV channel has apparently been jammed again around the country.
1814 GMT: Political Prisoner Watch - We share this report, translated by an opposition Facebook Page:
Saham News reports that Fakhrosadat Mohtashamipour, the wife of Mostafa Taajzadeh was arrested during the protests in Tehran today. Mohtashamipour apparently contacted her daughter by cell phone while being arrested. Mohtashamipour's daughter told Saham News: " I could hear my mother protesting to the anti riot police."
Fakhrosadat Mohtashamipour is the wife of Mostafa Tajzaadeh, one of Mir Hossein Mousavi's advisers during the 1999 presidential elections and former deputy interior minister during the reform period. She has written many letters to the authorities of the Islamic Republic protesting the illegal arrest and incarceration of her husband over the past one and a half years.
1754 GMT: Our second video of the day reportedly shows protesters and police in Mashhad, where there have been widespread clashes all day.
1744 GMT: The BBC has released a video, reportedly showing chants this evening in Shiraz. The protesters can be head chanting "Mubarak, Ben Ali, Now it's Time for Seyed Ali (Khamenei)."
1724 GMT: A Journalist, speaking to Kaleme, reported that he was "spattered in blood" after security fired shots into the crowd. Kaleme is calling today's security presence in Tehran, and the resulting violence, "unprecidented."
We have not yet verified these reports.
1717 GMT: RAHANA is reporting that there are heavy clashes on Ahmad Abad Street in Mashhad, hometown of Supreme Leader Ayatollah Ali Khamenei. Eyewtinesses there describe a tense situation where at least 150 people have been arrested.
1645 GMT: I am now handing back to James Miller, who will take you through the next few hours.
1635 GMT: Rafsanjani Watch. Meanwhile, the contest for the leadership of the Assembly of Experts heats up. The office of Hasehmi Rafsanjani, who holds the post, says recent anti-Rafsanjani propaganda is an insult to the 80 members of the Assembly.
Earlier today, influential MP Gholam-Reza Mesbahi-Moghaddam said --- incorrectly or mischievously --- that Rafsanjani was not standing for re-election but Ayatollah Mahdavi Kani, put forth by pro-Ahmadinejad opponents of Rafsanjani, would be standing.
1625 GMT: Activists say 50 people have been arrested at Enghelab Square.
1616 GMT: Saham News is reporting --- but now as "unconfirmed" --- that two security vans were set on fire by protestors at Enghelab Square.
1615 GMT: In Tehran, the number of protesters in Ferdowsi Square and Navab and Behboodi Streets is increasing.
1610 GMT: A witness in Isfahan says protests were silent and there was not much conflict with security forces.
1605 GMT: Mardomak reports that rallies are trying to form in Tabriz and Shiraz, but are being blocked by security forces.
A witness is reporting "mass arrests" in Tehran.
1557 GMT: Latest from BBC Persian includes a large demonstration in front of Kian Tire Factory and heavy security presence in Ahwaz in southern Iran.
The website also quotes a witness in Shiraz that there were clashes in front of Imam Hospital.
1550 GMT: According to Kalameh, protesters are gathered in Tehran’s Ferdowsi Square, Behboudi Street, and Navab Street.
Tehran witnesses report protesters disrobing cleric riding as passenger on motorbike near Azadi and Enghelab and chanting, “Khamenei is murderer! His authority is void!”
1545 GMT: Mardomak is reporting "body to body" confrontations along Enghelab Avenue.
Mehdi and Fatemeh Karroubi's son Mohammad Taghi has complained again about the "disgraceful" silence of the "war and revolution generation" regarding his parents' plight. He compared the regime's treatment of the Karroubis to those of the treatment by the Iraqi Baathist regime of the Sadr and Hakim families. That is an ominous comparison, as the Sadrs and Hakims, prominent Shi'i clerical families, have had several members murdered by Saddam Hussein's security forces.
1540 GMT: Dissected News reports from a source: "Students gathered in the cafeteria in the Yazd University to mark 1 March at 9:30 a.m. and took their protests to the university campus. Five minutes after the start of the gathering, 20 university guards attacked the students and seized their cameras. Classes were also not held in the morning in this university."
1535 GMT: Rah-e-Sabz reports at least 10 people arrested in Mashhad.
BBC Persian reports shots fired near Vanak Square in Tehran.
Tehran witness says protesters are chanting "Death to Dictator" near Azadi & Enghelab Avenues. There are also reports from HRANA of the same chants on Jamalzadeh Street, next to Tehran University.
1519 GMT: Deutsche Welle Persian has published an eyewitness account of a large, and still growing, crowd gathering in Tehran, despite teargas being used to try to disperse it. The most important line in the account, which has not been verified with other sources yet, might be this: the crowd near Enghelab Square is already larger than it was on 25 Bahman (14 February), according to the source.
According to Kaleme's latest report, less than an hour ago the crowd was still growing in Enghelab (Revolution) Square.
1506 GMT: There are many reports of clashes in front of Tehran University. GVF is reporting that there is a growing crowd at Vali Asr Square and Behboodi Avenue. Kaleme, a website closely linked to Karroubi, is depicting a very tense situation near Enghelab (Revolution) Square, where a large crowd of protesters is moving towards security forces. Eyewitnesses have told the BBC Persian that there is loud chanting at the Vesal Crossroads, where people are shouting "Ya Hossein, Mir Hossein," and "Ya Mehdi." One witness has described Tehran's streets as "packed."
There are now new (unconfirmed) reports of protests in Tabriz and Karaj as well.
Reuters is confirming that teargas has been used on protesters in Tehran.
1451 GMT: CNN's Reza Sayah is reporting a large scale security presence on the streets of Tehran. So far, he has not confirmed any of the other information about potential protests.
Protests appear to be escalating in Tehran. This report from the Tehran Bureau:
6:10 p.m. Eyewitnesses tell BBC Persian that people created an artificial traffic congestion in Resalat Avenue to halt the advance of riot police and Basij. Bardia on EPersian says he is at the intersection of Vali Asr and Enghelab and that tear gas has been fired there. Ferdowsi Square has been closed off by police. People have gotten out of their cars and are walking westward down Enghelab toward Azadi Square.
1421 GMT: KICKOFF!! The Asia Cup soccer match (Esteghlal v. Qatar) has just started in Azadi stadium. Multiple sources have reported that the regime is extremely worried that the fans (100,000 of them) might join the protests when the game is let out, or that they will chant anti-regime slogans. They have prepared to mute the audio.
According to the Human Rights News Agency, protesters are gathering in Namazi Square in Shiraz.
Homylafayette, a reliable source has this report on Twitter: "Eyewitness tells DeutscheWelle: Security in Vali Asr less than Feb 14, but higher in side streets."
1347 GMT: RAHANA is reporting that protesters are gathering in the city of Shiraz, where a large security presence is also felt.
BBC Persian is also reporting that there are protesters gathering on Vesal Street, just north of Enghelab. According to their liveblog, people are honking their horns and shouting "dictator" in central Tehran.
PeykeIran describes Tehran as being in a state of "undeclared martial law."
1327 GMT: A reliable source in the past has just reported that four people were arrested on Keshavarz boulevard. We cannot confirm this.
An eyewtiness has told the BBC Persian that protesters have started to gather at the Karim Khan bridge.
1310 GMT: Our sources - heavy security, people on the streets with umbrellas shopping for Nowrooz (Persian New Year) but still no protests. Protests are not expected to begin until 5 PM local time (20 minutes)
1254 GMT: RAHANA sums up the current situation in Tehran poignantly: "Tehran has once again become a barracks."
James Miller (Dissected News) will be covering the updates while Scott is detained.
1240 GMT: Eyewitnesses report a heavy security presence in 7 Tir Square in Tehran, with security forces based near a mosque.
RAHANA is reporting significant security presence in all major intersections and squares in Tehran.
1205 GMT: The Arrests. Iran Prosecutor General Gholam-Hossein Mohseni-Ejei has again denied that Mir Hossein Mousavi, Zahra Rahnavard, and Mehdi and Fatemeh Karroubi have been arrested.
1200 GMT: BBC Persian is quoting eyewitnesses that riot vans have been deployed around Enghelab Square in Tehran.
1140 GMT: An Earlier March. A Parliamentary committee will issue its report on the protests of 14 February (25 Bahman) tomorrow.
On 25 Bahman, tens of thousands of demonstrators appeared on Iran's streets for the first time in more than a year. Two protesters were killed.
The regime is trying to portray the marches as those of a few supporters of Mir Hossein Mousavi and Mehdi Karroubi and of the "terrorist" Mujahedin-e-Khalq.
1130 GMT: The Arrests. A group of Iranian activists has written to United Nations Secretary-General Ban Ki-Moon to urge his intervention for the freeing of Mir Hossein Mousavi, Zahra Rahnavard, and Mehdi and Fatemeh Karroubi.
1125 GMT: Campus Watch. Mardomak reports that Tehran University has cancelled a number of classes today on the advice of security forces.
1120 GMT: 10 Esfand. Detained filmmaker Mohammad Reza Nourizad has put out a letter of support for today's marches, declaring that demonstrators "have proven their survival with a cry of protest".
1110 GMT: Political Prisoner Watch. Qazvin University student Ali Bayani was arrested this week for promoting today’s protests. Qazvin Professor Reza Isadi is reported missing.
1010 GMT: 10 Esfand. Activists are circulating a letter from political prisoners in Rajai Shahr Prison supporting today's protests and "struggle against the regime".
1000 GMT. Within the Government. News of an interesting political move in Fars....
"Informed sources" have told the website that President Ahmadinejad may be planning to replace his controversial 1st Vice President Mohammad Reza Rahimi.
Rahimi has been under sustained attack from some members of Parliament since his appointment in autumn 2009. He is accused of exaggerating his academic credentials and of being involved in a massive insurance fraud. The file on the fraud case has been passed by Iran's judiciary to prosecutors.
0950 GMT: BBC Persian reports that Internet speed is normal in Tehran. BBC Persian's television service has been jammed and cut off in parts of north Tehran, however, and an EA source reports wide-spread destruction of satellite dishes by security forces.
0940 GMT: The Arrests. Opposition advisor Mojtaba Vahedi has claimed in an interview that Mojtaba Khamenei, the son of the Supreme Leader, played a key role in the decision to arrest Mir Hossein Mousavi, Zahra Rahnavard, and Mehdi and Fatemeh Karroubi on Thursday night.
Vahedi asserted that Iran's judiciary, headed by Sadegh Larijani, was against the move but was overruled by the Supreme Leader's office.
0610 GMT: CyberBravery. Saeed Valadbaygi, the man behind A Street Journalist and a leading Web activist before and after his forced departure from Iran, tells Index on Censorship of his coverage of the last opposition on 20 February:
As well as bringing the site down, four members of our team received emails, with the following threat: "We have hacked you. This is your first warning. If you continue there may be a hefty price — physically and socially — we will stop you."...
We will continue our work but with no budget we are limited. Our strength is the capability of our team. We need support from partnerships and the financial support of larger media to cover our weaknesses. Things are different now. It’s not difficult to get the site back up, but we need to investigate how the government are operating and take more precautions for our personal security. We recognise that they’re not joking.
0600 GMT: Pedestrian posts this photograph and comments:
The painter is lost … Somewhere in Tehran’s murky, uncharted underground. It’s not the first time that we lose people to the underground. It will certainly not be the last. But because of him, and because of them, to slavery we will never return.
“Just as the earth can never die, neither will those who have ever been free return to slavery. The fascists may spread over the land, blasting their way with weight of metal brought from other countries. They may advance aided by traitors and by cowards. They may destroy cities and villages and try to hold the people in slavery. But you cannot hold any people in slavery.” --- On the American Dead in Spain, Ernest Hemingway
0555 GMT: Rafsanjani Watch. On the eve of the election for head of the Assembly of Experts, Hashemi Rafsanjani has reportedly told four conservative politicians that there are three "red lines" he will not cross: the issue of the regime, velayat-e faqih (clerical supremacy), and the Supreme Leader.
0545 GMT: The Arrests. Some direct overseas reaction to the detention of Mir Hossein Mousavi, Zahra Rahnavard, and Mehdi and Fatemeh Karroubi --- Germany reportedly summoned the Iranian Charge d'Affaires to complain, and Swedish Foreign Minister Carl Bildt used Twitter to send the message, "Most worrying reports of arrests of opposition leaders in Teheran. The EU [European Union] must and will react."
0530 GMT: And so we reach a potentially significant convergence. The regime has now made the leap, considered but rejected for many months, of arresting leading opposition figures. Mir Hossein Mousavi, Zahra Rahnavard, and Mehdi and Fatemeh Karroubi are reportedly detained in a military prison in Tehran, although no charges have been filed and State media are not acknowledging the arrests.
Even before the arrests, while Mousavi, the Karroubis, and Rahnavard were confined to their house, the opposition had called on its supporters to march today, following up the rallies of 14 and 20 February. Now that call takes on an added significance, as a sign of defiance of the regime's escalated repression.
The opposition has faced the challenge of pulling this off despite being scattered by detentions and limited in communications. Still, there is chatter this morning that people know of the call and will respond. A source tells us that of a family in Iran --- not in Tehran, but in the countryside --- who, for the first time, made a political statement. They did so in code, speaking about a rainstorm and adding, "Watch the forecast as it is going to be huge."
And there is a third important development which is accelerating. President Ahmadinejad's supporters are pushing their campaign to remove former President Hashemi Rafsanjani as head of the Assembly of Experts tomorrow. Significantly, the top story in the pro-Ahmadinejad Islamic Republic News Agency this morning is an interview with a spokesman of the conservative Society of Combatant Clergy who says, "Ayatollah Mahdavi Kani is the best choice for President of the Assembly."
Mahdavi Kani confirmed yesterday that he would stand for election tomorrow.