The third, identified as N. A., was said to be a member of People’s Mujahedeen of Iran, an exile group that Iran says works to overthrow the government.

The news of death sentences sparked immediate condemnation from international human rights groups. In the weeks after the election, millions of Iranians marched in the streets of Tehran, charging that Mr. Ahmadinejad stole the race. At least 30 people were killed in a government crackdown that quelled the protests but failed to end the simmering discontent.

“Zamani’s trial was a mockery of justice,” the executive director of Amnesty International USA, Larry Cox, said in a statement. “To impose the death sentence is beyond deplorable. Iran should immediately rescind this sentence.”

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The ISNA report, without giving details, said the court also sentenced 18 other protesters. That raised concerns about the hundreds of journalists, former government officials, academics and protesters still held in prison, many incommunicado, said the International Campaign for Human Rights in Iran, a group based in the United States.

There have been many charges of protesters’ being tortured while in prison, and the government has agreed that some prisoners were abused, although it has continued to dispute accusations that some were raped and sodomized.

“Iranian authorities have released little or no information about many of the approximately 400 persons who remain detained,” the human rights campaign said in a statement, adding that Iran was “violating international standards for due process and raising deep concerns about their health and safety.”

Among those who remain in detention are Maziar Bahari, a filmmaker and reporter for Newsweek, and Shapur Kazemi, the brother-in-law of Mir Hussein Moussavi, who the opposition claims won the election. Mr. Kazemi, 62, is a respected telecommunications engineer and is known for his activities in technical and economic fields rather than for political activism.

Others who are still being held include the former vice president, Mohammad Ali Abtahi; Muhammad Atrianfar, a publisher and confidant of the former president Ali Akbar Hashemi Rafsanjani; Mostafa Tajzadeh, a deputy interior minister in the reformist government of the former president Mohammad Khatami; Saeed Leylaz, an economist and former government official; and the journalist Isa Saharkhiz, who according to Iranian news reports suffered broken ribs during interrogation.

Student activists being held include Abdullah Momeni, a former spokesman for the student group Iran Alumni Association, who confessed in court. Mr. Momeni’s wife says he had been badly tortured, according to Iranian news reports.