The Iranian authorities declare victory for President Ahmadinejad; candidates Mir Hossein Mousavi and Mehdi Karroubi challenge results; protests begin amid reports of detentions by security forces
2230 GMT: We're signing off until the morning. Thanks to everyone who sent us information today. To friends in Iran: our thoughts are with you.
2200 GMT: We have now posted the English translation of the letter released by Mir Hossein Mousavi to his supporters this afternoon.l
2145 GMT: In addition to the video of this afternoon's protests in Tehran, which we posted in this entry, we now have posted footage that the riots have spread this evening to the university in Shiraz and to the city of Mashhad..
2000 GMT: Juan Cole has posted a thoughtful analysis, "Top Pieces of Evidence that the Iranian Presidential Election Was Stolen", with re-construction of how the process might have unfolded. We have posted it in a separate entry.
1930 GMT: Mobile phone service was cut almost two hours ago. Many Iranians are now relying on the Internet for information, but there are concerns that this might be disrupted tomorrow. BBC Persian has now been blocked.
Some streets are still crowded with demonstrators shouting for Mousavi.
1740 GMT: President Ahmadinejad now addressing the nation. CNN has live feed. At times, CNN International television is going split-screen, putting Press TV's pictures Ahmadinejad address side-by-side with footage of demonstrations.
1735 GMT: A pro-Mousavi Twitter user suggests a way to access Facebook from Iran.
1715 GMT: An (unverified) story that we heard two hours ago is now circulating widely: Ministry of Interior officials called the Mousavi campaign to inform them of their candidate's victory. Mousavi was to write a victory speech, and a celebration was to be held Sunday (which, indeed, is what the Ahmadinejad campaign is now planning).
Shortly afterwards, however, the "information" was withdrawn without explanation.
1710 GMT: The correspondent for the American television network ABC reports that security forces have confiscated his crew's camera and videotapes. They are now shooting footage on cellphones.
1700 GMT: Facebook is blocked and SMS/texting systems are still out of service. Clashes continue between demonstrators and security forces around the Ministry of the Interior.
A correspondent notes that while the Supreme Leader has moved with unprecedented haste to endorse the election outcome (under Iranian law, the process is supposed to take at least three days), Iran's Guardian Council has not ratified the results nor has the Speaker of the Parliament, Ali Larijani, congratulated Ahmadinejad.
There are reports that Mousavi, Karroubi, and former President Mohammad Khatami are gathering at the house of former President Hashemi Rafsanjani.
1640 GMT:A notable split is emerging in Western coverage between those who are ready to call the election rigged, such as Robert Dreyfuss in The Nation publishing the opinion of former Foreign Minister Ibrahim Yazdi on an Ahmadinejad "coup d'etat", and those who claim that Ahmadinejad's landslide should have been foreseen, such as Abbas Barzegar in The Guardian.
Mehdi Karrubi's campaign manager is providing updates via Twitter.
530 GMT: The Flickr stream of Mir Hossein Mousavi is carrying a number of photos of violent clashes between police and demonstrators in Tehran.
1500 GMT: Government websites put Ahmadinejad's vote at 22 million and Mousavi's at 11 million.
Both Mir Hossein Mousavi and Mehdi Karroubi have said that this is "the beginning of events" and they will stand up "to the end". Attention now turns to the statement of the Supreme Leader, Ayatollah Khamenei.
There are reports of closing of streets near the Interior Ministry and detentions by military forces. Some people working in Tehran are afraid to return to their homes.
Press TV English, which had provided relatively open coverage of the election, is saying nothing about today's tension over the outcome.
There are reports of clashes around the Ministry of Interior between demonstrators, police, security forces, and Basiji (unofficial security units).
0830 GMT: To limit the possibility of demonstrations, universities are closed. There are military forces scattered throughout Tehran. Some websites, including the BBC English-language site, have been blocked.
The official overseeing elections will shortly be speaking. More importantly, Mir Hossein Mousavi will be making a statement in the next few hours.
Pro-Mousavi correspondents from Tehran write of "a state of shock" at the outcome. One says simply, "Iran is mourning today."
0200 GMT, 13 JUNE: BBC reports that Mahmoud Ahmadinejad has so far 66 percent of the vote. Officials say that almost 70 percent of votes has been counted.
1800 GMT Iranian election officials are calling the voter turnout "unprecedented", with queues of up to three hours. Polling stations were kept open an extra three hours.
In Washington, President Obama said that the choice of President was "up to the Iranian people" but added that he hoped for "possibilities of change". In a far from coded reference, he said that he hoped the Iranian outcome would follow the example set by Lebanon on Monday.
1700 GMT: Voting has been extended by three hours (to 9pm local time) due to the heavy turnout, according to the BBC.
1300 GMT, 12 JUNE: Turnout is very heavy throughout the country. An EA correspondent reports from north Tehran that there is an intensity and excitement in the public mood. Other correspondents report high expectations and hopes that there will be no "disruptions" in the count.
Government authorities are trying to damp down speculation of any altering of the result. The Intelligence Minister says that there have been no reports of electoral breaches while the head of the Parties' Desk declared that any reported misconduct would be dealt with swiftly. Amidst reports of 10 million phone texts being sent in recent days, the Telecommunications Ministry says it is investigating reports of disruption to SMS service.
Senior politicians and clerics are calling both for high turnout and fair conduct to hold up Iran as an example to the world. Candidate Mehdi Karroubi has called for tonight's decision to have the "respect of the nation".