At least 10 people were killed and more than 100 wounded when police clashed with "terrorists" in Tehran on Saturday, state TV says.
It said "rioters" set two petrol stations and a mosque on fire and attacked a military post, during protests over disputed elections.
State TV earlier said 13 had died, but the toll was then reduced.
The reports cannot be verified as foreign media in Iran are being severely restricted, BBC reported.
State media said calm had returned to Tehran on Sunday.
It was unclear whether fresh protests would go ahead, after official demands for them to stop.
The protests were sparked by disputed presidential elections, but have since escalated into a political crisis for the establishment.
The state TV report said 10 people had been killed in clashes between police and "terrorist groups" in Tehran, and added "rioters" had set two gas stations on fire and attacked a military post.
Earlier it said an unspecified number of people had died when "rioters" set a mosque on fire. But later reports said there had been no deaths at the mosque. A correction was also issued reducing the overall death toll to 10 from 13.
The BBC and other foreign media are subject to heavy restrictions which have prevented reporters from leaving their offices to confirm these reports.