One of Iran's most prominent pro-reform figures admitted fomenting unrest and asked for the country's forgiveness Tuesday, the latest confession in the mass trial of opposition activists detained in the postelection crackdown.

The opposition says defendants in the trial have been forced to make confessions and has denounced the proceedings as a "show trial" aimed at smearing their movement in the public eye.

Tuesday's session was the fourth in the trial of more than 100 opposition activists and protesters, Iran's biggest political trial in decades. The defendants — who include some of the country's biggest pro-reform politicians — are accused of trying to topple the Islamic clerical leadership through a "velvet revolution" of mass protests that erupted after the disputed June 12 presidential election.

The star defendant Tuesday was Saeed Hajjarian, who is considered the engineer of the pro-democracy reform program under former President Mohammad Khatami and is revered as a hero of the reform movement after he survived an assassination attempt in 2000. He was shot in the head from close range in the attack, leaving him partially paralyzed. He uses a wheelchair and has difficulty speaking.

Two people carried Hajjarian into the courtroom by the arms, the state news agency IRNA said. A prosecutor read out a long list of charges against him — among them, acting against national security, fomenting unrest, propagating against the ruling system, having contacts with British intelligence and insulting Supreme Leader Ayatollah Ali Khamenei. The prosecutor asked for the "full punishment" against Hajjarian, though officials have not said what the maximum sentence would entail.

Hajjarian identified himself to the court, then asked another defendant, Saeed Shariati, to read a text of his confessions on his behalf because of his inability to speak fluently.

"I've committed grave mistakes by offering incorrect analysis during the election ... I apologize to the dear Iranian nation because of my incorrect analyses that was the basis for many wrong actions," Hajjarian's text said, according to IRNA.

Hajjarian, a leftist thinker, renounced his own writings from the past 10 years and said his ideas "contradict the path of the Imam" — referring to Ayatollah Ruhollah Khomeini, the founder of Iran's Islamic Republic.

He admitted that his ideas had led his party — the Islamic Iran Participation Front, Iran's largest reformist party — "astray, particularly during the election." He and Shariati both announced their resignation from the party, which hard-liners have accused of fomenting unrest and demanded be dissolved.

Hajjarian was a top aide to Khatami, who was president from 1997-2005 and attempted to bring about social and political reforms in Iran — though ultimately the attempt was stymied by hard-liners who now dominate the government under President Mahmoud Ahmadinejad.

Hajjarian also served as a top intelligence official for about two decades before Khatami's administration and is often described as the "walking memory" of recent Iranian history because of his access to classified information and the Islamic establishment's secrets.

Many of those on trial held key positions during the administration of Khatami. Among the defendants in the courtroom on Tuesday were top reformists including former Deputy Interior Minister Mostafa Tajzadeh, former Deputy Foreign Minister Mohsen Aminzadeh and former government spokesman Abdollah Ramezanzadeh. Also there were Behzad Nabavi, a veteran politician known, as well as Saeed Leilaz, a prominent political analyst. All of them wore prison uniform and slippers.

Each of the previous three sessions, defendants have been brought forward and gave sweeping confessions, often completely renouncing their long careers as reformists and adopting the government's line that they organized the postelection protests at the behest of Iran's foreign enemies to bring down the Islamic Republic.

The opposition says the confessions were forced through abuse when the defendants were held for weeks in prisons with no communication with either family or lawyers.

Hundreds of thousands of Iranians marched in mass demonstrations for days after the election, claiming the official results were rigged in Ahmadinejad's favor and Mousavi was the true winner. Security forces, including the Revolutionary Guard and Basij militia, crushed the protests in a heavy crackdown in which hundreds were arrested. The opposition says at least 69 were killed and that many detainees were tortured or abused in prison.