The trial has begun in Iran of 100 people arrested for their alleged involvement in post-election violence.
The charges included rioting, vandalism, "acting against national security", and conspiring against the ruling system, state media reported.
Those on trial included members of the opposition reform movement, including a former vice-president.
Pro-government media reported what they say were confessions by some of the leading reformists.
But the leading reformist party Mosharekat described the proceedings as a laughable show trial and said the confessions had been forced.
The first court session has now ended and it is not clear when the next will be held.
Some of the accused, who had allegedly accepted the charge of treason, told the court their earlier claims of fraud during the 12 June poll were baseless, official media said.
Allegations of vote-rigging were made by defeated candidates and their supporters as soon as it became clear the president had been re-elected by a large margin.
Mohammad Ali Abtahi (left): former vice-president, member of the Assembly of Combatant Clerics
Mohsen Mirdamadi (centre): leader of the biggest reformist party, the Islamic Iran Participation Front
Behzad Nabavi (right): member of the central council of the Organisation of the Mujahideen of the Islamic Revolution, former industry minister and former vice speaker of parliament
Mohsen Aminzadeh: former deputy foreign minister, served under reformist president Mohammad Khatami, member of Islamic Iran Participation Front
Former vice-president Mohammad Ali Abtahi was quoted by Fars news agency as telling the court: "I say to all my friends and all friends who hear us, that the issue of fraud in Iran was a lie and was brought up to create riots."
Another of the accused, Mohammad Atrianfar, was quoted as saying that they should all submit to the law.
"We mistook certain irregularities [in the vote] as fraud," Fars quoted him as saying.
At the trial, pictures from the packed courtroom showed seated defendants wearing prison uniforms and with guards next to them.
Foreign media, including the BBC, have been restricted in their coverage of Iran since the election protests turned violent.
The BBC's Kasra Naji, in London, says the timing and scale of the trial came as a surprise and suggests Iran's leadership wanted to send a message to stop any more protests.
But judging from messages on micro-blogging site twitter and the internet, our correspondent says, the move may have the opposite effect, with several people talking about the need for new demonstrations and calling those on trial "national heroes".
Official news agency Irna said other charges against them included "having ties with counter-revolutionary groups."
Some of those on trial had been photographed "committing the crimes", and their accomplices were "on the run", Irna reported, without specifying the number of people on trial.
The defendants included supporters of opposition leaders Mir Hossein Mousavi and Mehdi Karroubi - both defeated in the election - and aides of former reformist president Mohammad Khatami.
Fars news agency reported that former deputy foreign minister Mohsen Aminzadeh, former government spokesman Abdollah Ramazanzadeh, former senior lawmaker Mohsen Mirdamadi and former Industry Minister Behzad Nabavi were among the defendants.
The protests were the largest mass demonstrations seen in Iran since the 1979 revolution which brought the current Islamic regime to power.
12 June Presidential election saw incumbent Mahmoud Ahmadinejad re-elected with 63% of vote
Main challenger Mir Hossein Mousavi called for result to be annulled, alleging poll fraud
Mass street protests saw at least 30 people killed and foreign media restricted
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