Accounts emerged from released prisoners about beatings and brutality during their detention. One told of being crammed with 200 other protesters in a pitch-black cell as guards waded in, beating them. Another said he and other detainees were forced to lick toilet bowls.
In recent days, there have been several deaths of young activists in prison - including the son of a prominent conservative. The announcement of trials is likely to anger the opposition, which says that detainees are being tortured into making false confessions to be used against them in court.
Opposition leader Mir Hossein Mousavi is to lead a ceremony on Thursday for those who have died in the postelection crackdown - and the memorial could turn into a new confrontation between protesters and security forces. It is timed to coincide with the passing of 40 days since the death of Nada Agha Soltan, a young woman who was shot to death during a protest. Video of her dying moments made her an icon to the protest movement.
Mousavi and fellow pro-reform leader Mahdi Karroubi will hold the ceremony in Behesht-e Zahra - the large cemetery on Tehran's southern outskirts where some slain protesters have been buried - after authorities rejected his request to hold it at Tehran's main Mosalla mosque, Karroubi's Web site reported.
Hundreds were arrested in the crackdown against protests by hundreds of thousands of opposition supporters, who claim that the June 12 presidential election was fraudulent and that Mousavi - not hard-line incumbent Mahmoud Ahmadinejad - was the victor. Among those detained were young protesters, but also senior pro-reform politicians and prominent rights activists.
The state news agency IRNA said Wednesday that indictments had been issued against "around 20" detainees involved in "planning and carrying out sabotage" and that trials will begin on Saturday. Among the defendants are some who had contact with the Mujahedeen-e Khalq - a dissident group of Iranian exiles - and members of the Bahai faith, who are often targeted by the Iranian government, IRNA said.
They will face charges including connections to terrorist groups, planting bombs, carrying weapons and grenades, intentional attack on the police and Basij, attacking security and university facilities, "sending images to the media of the enemy" ... and damaging public property, IRNA said.
The report said this was the "first phase" of trials, and that in later phases the defendants would be "those who ordered the post election unrest," an apparent reference to opposition politicians.
On Tuesday, 140 postelection detainees were released from Tehran's Evin prison in an attempt by Iran's leadership to try to ease the uproar over prisoners. At the same time, Supreme Leader Ayatollah Ali Khamenei ordered the closure of Kahrizak prison, a facility on the capital's southern edges where several detainees were reported to have died from abuse.
But even some in the conservative camp that backs Khamenei and Ahmadinejad said that was not enough and that those behind the abuse should be punished.
"Some died after detention due to beating. Officials said two victims died due to meningitis.It should be reviewed and oppressors should be identified and prosecuted," Ahmad Tavakkoli, a prominent conservative lawmaker, said, according to the opposition Web site Mowjcamp.
Tavakkoli said "individuals without permits" had attacked university dorms and homes - a reference to plainclothes attackers believed to be connected to the Basij militia. "They and their organizers and supporters should be identified," he said.
Accounts from released prisoners appeared on opposition Web sites this week, describing beatings and other abuse at the hands of guards and interrogators.
One told of being held at Kahrizak since his arrest in a July 9 protest, saying, "We were at least 200 people in one room, and everyone was getting beatings with sticks." He wrote that at one point the guards turned out the lights and beat the prisoners for a half hour. The protester, who said he was released on Monday, listed the names of six prisoners he believed had died during the assaults.
As in other prisoner accounts, he wrote anonymously because he had been told not to speak of his detention. His and the other accounts could not be independently confirmed.
Another released prisoner said he was taken to a police station and beaten, and then he and others were forced to lie down in a bathroom, tied their legs up behind their backs and forced them to lick a toilet.
The opposition has been complaining for weeks about abuse in prisons, saying that many are being held in secret locations by the elite Revolutionary Guards, Basij or other unknown bodies. But authorities began paying attention after the son of Abdolhossein Rouhalamini, a prominent conservative, was killed in prison, reportedly at Kahrizak.
A powerful conservative lawmaker, Ali Mottahari, said closing Kahrizak was not enough and that "those responsible for detahs in prison like that of the late Rouhalamini must be identified." He said those involved in abuse at Kahrizak could now be at other facilities.
He reprimanded government officials, asking, "Why did things reach a point that the supreme leader had to get involved? If they had followed their own positions on human rights, the supreme leader's entry wouldn't be necessary."
Several of the top clerics in Shia Islam - the "marajeh-e-taghlid," or "objects of emulation" - have also issued statements in recent days condemning abuses of prisoners.