This is the first time the former president will speak in public since last month’s presidential election.
During the campaign Ahmadinejad said that he would take action against the former president’s business empire.
Rafsanjani’s children took part in demonstrations calling for the annulment of “rigged” elections. Other relatives were also arrested and released a few hours later.
Tomorrow’s event is also the first time that Mousavi appears in public following demonstrations he encouraged against Khamenei and Ahmadinejad, which ended in 20 dead, hundreds of wounded and arrests.
Mousavi’s supporters are reportedly planning to go to Friday prayers at Tehran University which are regularly attended by Islamic Republic hardliners, setting the stage for a possible confrontation.
Almost a month ago Khamenei spoke at this same venue warning opposition leaders that they would be held responsible for inciting protest.
Iran’s leading hard-line newspaper Kayhan warned against “provocation” at the Friday prayers.
“According to reliable sources tomorrow some people want to incite conflicts at the Friday prayers,” writes newspaper editor Hossein Shariatmadari.
Others are saying instead that the Friday prayer might be used to declare a temporary truce between Rafsanjani and Ahmadinejad.
Defeated candidate Mousavi said he would continue his opposition within the country’s “legal framework”.
Demonstrations in June marked a critical point in the 30-year history of the Islamic Republic.
They showed a growing loss of confidence in the population towards Iran’s leadership and important divisions among ruling elites.