Hundreds of protesters, politicians and activists have been detained in Iran after mass protests over the disputed re-election of Mahmoud Ahmadinejad, the Iranian president.
Hadi Ghaemi, the director of the New York-based International Campaign for Human Rights in Iran, said on Thursday that he had been told that about 200 people were being held across the country.
He told the Associated Press news agency that he had spoken to family members and colleagues of people who had been arrested or had disappeared.
Supporters of Mir Hossein Mousavi, a defeated reformist candidate, have staged demonstrations every day since Ahmadinejad was declared to have won the presidential election by a landslide.
Iran's intelligence ministry has said that it has arrested a number of "main agents" behind the clashes which broke out during some of the protests in the capital, Tehran, the state-run Press TV said on its website on Thursday.
"The intelligence ministry has identified and arrested a number of the main agents and elements behind acts of vandalism in recent days in Tehran," it quoted Gholamhossein Mohseni Ejei, the intelligence minister, as saying.
Reports on Thursday said that Ebrahim Yazdi and Mohammad Tavasoli, leaders of Iran's banned Freedom movement, had been arrested.
Ghaemi said that Yazdi had been taken from a hospital emergency unit where he was undergoing checks for stomach problems.
Yazdi, who was the foreign minister in the first government after the Islamic revolution in 1979, told the Reuters news agency on Monday that the dispute over the June 12 poll had revealed deep divisions in Iran's establishment and warned of worsening "political suppression".
Other prominent reformists including Saeed Hajjarian, an adviser to Mohammad Khatami, a former president, and Abdolah Ramezanzadeh, a former spokesman for Khatami, are reported to have been detained in recent days.
The International Campaign for Human Rights in Iran said that students leaders and journalists had also been arrested.
"We have no information about what's going on, where they are being held," Al Jazeera's Alireza Ronaghi, reporting from Tehran, said.
"Some of the information comes out on the websites that are not being filtered yet and some of the details of the arrests appear in the papers the next day.
"The families have been trying to convince the Revolutionary Courts to release them."