Alireza Beheshti, a senior aide of the main opposition leader Mir Hossein Mousavi, and Morteza Alviri, former Tehran mayor and top aide of the reformist Mehdi Karroubi, were arrested over the past two days, mowjcamp.com reported.
News of their arrests came soon after ILNA news agency reported on Tuesday that authorities had raided the office of Karroubi himself and even arrested the chief editor of the website of his political party, Etemad Melli.
It also came as Iran prepared to hand over an updated package of proposals to resolve the standoff over its controversial nuclear programme to Tehran representatives of the major powers.
Britain, China, France, Germany, Russia and the United States have given Iran a late September deadline to open talks on the nuclear issue or risk new UN sanctions.
Another reformist website, Norooznews, reported that authorities had sealed the office of prominent dissident Emadeddin Baghi's group, the Society to Defend Prisoners' Rights.
It said that property was also confiscated during the raid on the established non-governmental organisation.
Beheshti, who recently said that 72 people died during the unrest which erupted after the re-election of Ahmadinejad, was arrested on Tuesday after his office too was raided on Monday, mowjcamp said.
His office had followed up the cases of those detained or injured in the post-election unrest. Iranian officials say about 30 people were killed.
Iran has carried out repeated crackdowns on opposition groups who continue to dispute Ahmadinejad's victory in the June 12 presidential election.
In the initial post-election crackdown, security forces arrested some 4,000 people. Most have now been released but around 140 have been put on mass trials.
Reformist media said the arrest of Beheshti and Alviri took on added significance in the light of sustained claims by the opposition that some of those detained in the post-election unrest had been raped or tortured in custody.
Karroubi himself has been the most vocal in airing charges that both male and female detainees were raped, allegations that have been repeatedly denied by Iranian officials.
On August 17, following Karroubi's accusations the judiciary banned his party newspaper, also called Etemad Melli.
But on Wednesday judiciary chief Sadeq Larijani acknowledged that there had been some abuses of detainees which he said were being investigated with a view to possible prosecution.
"Some offences occurred while dealing with riots and some offences in jails have hurt the reputation of the regime," the official IRNA news agency quoted Larijani as saying.
"These things are being carefully pursued in the judiciary," he added.
On Tuesday, Karroubi's office was raided by authorities, his party spokesman Esmaeel Gerami Moghaddam told the ILNA news agency.
Mehdi Karroubi's "office was sealed by order of the Tehran prosecutor after a number of agents with a prosecutor's warrant came to his office near the Saadabad Palace in north Tehran," said Moghaddam.
"They searched the premises and collected documents, CDs, computers and films," he said. "They also arrested the chief editor of the Etemad Melli website."
Meanwhile, Iran's police chief warned on Tuesday against using the annual pro-Palestinian Quds Day march to stage anti-Ahmadinejad protests.
Karroubi had vowed that his supporters would come out in force on the day, and Mousavi has also called for continued civil disobedience.
The event, first held in Iran but now marked in other places as well, is to express solidarity with the Palestinian people. This year it will be held on September 18.
