Five detainees that Iran plans to put on trial in connection with anti-government protests last month are members of the armed People's Mujahideen Organisation of Iran (PMOI), a state news agency said on Friday.
The PMOI is an exile group opposed to Iran's Islamic system of government, Reuters reported.
It is the main faction of the Paris-based National Council of Resistance of Iran (NCRI), which has thousands of followers in Europe and the United States and was the first group to expose Iran's covert nuclear programme in 2002.
Last year the gorup was removed from a European Union list of banned terrorist groups but it remains on a separate U.S. list.
"The five accused whose files have been sent to revolutionary court under the charge of 'moharebeh' are members of the counterrevolutionary terrorist group," Tehran general prosecutor Abbas Jafari Dolatabadi was cited on IRNA as saying, in referring to the People's Mujahideen group.
IRNA said on Thursday that five unidentified detainees would face the charge of 'moharebeh', an Islamic term meaning warring against God that carries the death sentence.
Eight people were killed in clashes between security forces and supporters of opposition leader Mirhossein Mousavi on Ashura, the day of ritual Shi'ite mourning that fell on Dec. 27.
It was the worst violence since protests in the immediate aftermath of a disputed presidential election in June.
Supporters of Mousavi and Mehdi Karoubi, who both lost to President Mahmoud Ahmadinejad in the vote, say the result was rigged. Authorities deny the allegations.
Dolatabadi said some members of the outlawed Baha'i faith who were under arrest in connection with the Dec. 27 riots had played a role in organising the protests.
"These individuals were arrested both for organising Ashura riots as well as playing an effective role in the dispatch of pictures of Ashura riots abroad," he said.
The opposition website Rahesabz said on Wednesday that more than 180 people, including 17 journalists, 10 Mousavi aides and some members of the outlawed Baha'i faith, had been arrested in the aftermath of the protests.
The stakes are high because Ahmadinejad has championed a nuclear energy policy that has led the country, a major oil producer, into diplomatic conflict with the West, incurring U.N. sanctions on a stretched economy.
Iran rejects U.S. allegations it plans to develop nuclear weapons, saying its programme is peaceful and intended to produce electricity.