Iranian state television said 13 people had been killed in clashes between police and "terrorist groups" in Tehran, in an apparent reference to street unrest in the capital.
Iran's English-language Press TV also said "rioters" had set two gas stations on fire and attacked a military post.
"Thirteen people killed in police clashes with terrorist groups in Tehran," it said in a headline.
State television earlier said Iran's Intelligence Ministry had arrested members of an exiled opposition group it acccused of "terrorist activities" including setting buses on fire and destroying public property.