A total of 500 are reported to have been detained across the country, including well-known political figures from the 1979 Islamic revolution. The mass detentions combined with paramilitary raids on university campuses appeared to be part of a determined and sustained backlash on the part of a government that initially appeared to have been taken by surprise by the scale of the protests after the declaration that President Mahmoud Ahmadinejad had won Friday's presidential poll.
The authorities also launched what appeared to be a concerted campaign to link the protests with foreign intervention, calling in the US and British ambassadors to complain about what Tehran called "intolerable" meddling in Iran's internal affairs.
Ebrahim Yazdi, a former foreign minister and aide to Ruhollah Khomeini, was arrested at the Tehran hospital where he was undergoing medical tests, according to the website of his Freedom party. Seven other members of the party were also detained.
With the exception of Yazdi, the arrests appeared to bypass political leaders and focus on their lieutenants. Mohammad Tavassali, Tehran's mayor in the years after the Islamic revolution and leading member of the Kargozaran party was arrested. Tavassali is close to the former president, Hashemi Rafsanjani, who is the most powerful opposition within the inner circles of the clerical hierarchy.
Another former revolutionary stalwart, Behzad Nabavi, who negotiated with the US during the 1979-81 Tehran embassy hostage crisis, also appeared on the list of detainees.
"Iranian intelligence and security forces are using the public protests to engage in what appears to be a major purge of reform-oriented individuals whose situations in detention could be life-threatening," said Aaron Rhodes, a spokesman for the international campaign for human rights in Iran.
The wave of detentions has spread beyond the capital to include provincial cities. At least 100 civic figures are understood to have been arrested in Tabriz, where Mousavi has strong support.
Amnesty International reported that the detainees included 17 political activists, who had been "taken to unspecified locations on Monday night after they staged a peaceful protest in the city's Abresan Square".
The Tabriz detainees included Freedom Movement activists and eight members of the Islamic Participation Front, a reformist organisation linked to Khatami, were also arrested.
In Shiraz, in the south of the country, Amnesty cited reports said that a hundred students had been detained after security forces used teargas to storm the university library.
In the central province of Isfahan, a senior prosecutor warned that dissidents could face execution under Islamic law. "We warn the few elements controlled by foreigners who try to disrupt domestic security by inciting individuals to destroy and to commit arson that the Islamic penal code for such individuals waging war against God is execution," Habibi said, according to the Fars news agency.
Another four activists in Qazvin province, north of Tehran, were said by human rights campaigners to have "disappeared" while members of the Tahkim-e Vahdat, an influential students organisation supporting the other reformist candidate Mehdi Karoubi, had been "systematically targeted".
Human rights groups voiced concern over the health of a political activist, Saeed Hajarian, who was arrested yesterday. Hajarian, once an adviser to President Mohammad Khatami, needs constant medical attention for brain and spinal injuries sustained in a failed assassination attempt nine years ago.
Mohammadreza Jalaeipour, the son of a prominent Tehran academic and a Mousavi supporter was also reported to have been arrested as he was boarding a flight to London this morning.
Abdolfattah Soltani, a human rights lawyer who has defended many student activists, was picked up on Tuesday.
The new arrests follow an estimated 120 activists and journalists picked up in a first wave in Tehran over the weekend, including Mohammad Reza Khatami, brother of the former president, who was later released.
Two other prominent reformists, Mohammad Ali Abtahi and Behzad Nabavi, and a well-known human rights lawyer, were picked up in the same sweep.
It would seem that the backlash has begun. It may be (and I pray that it is the case) that the protests have reached an unstoppable critical mass. We shall see....