Iran banned a gathering on Sunday reportedly by supporters of opposition leader Mir Hossein Mousavi to mark the death anniversary of prominent revolutionaries killed in a bombing 28 years ago, the official IRNA news agency reported.
"No permit has been issued for any gathering today at Ghoba mosque" in Tehran, city governor Hossein Tala told IRNA, adding that no such request had been submitted.
IRNA said "some websites linked with the defeated electoral movement had said there would be a gathering at the mosque at 6 pm (1330 GMT)."
Prominent cleric Ayatollah Mohammad Hosseini Beheshti and more than 70 members of the Islamic Republic party were killed in a bombing on the party's headquarters on June 28, 1981.
The ILNA news agency reported that the Beheshti family was due to hold a ceremony at the mosque for two hours from 6 pm.
Iran has named a main Tehran square after the incident and state-sponsored commemorations are held every year.
Beheshti's son Alireza is a key ally of moderate candidate Mousavi, who has challenged President Mahmoud Ahmadinejad's victory in the June 12 election which opposition leaders have branded as rigged.