Access to the popular photo sharing and messaging apps Instagram and Telegram was restricted on mobile phones, Iranian media reported on Sunday, after three days of protests in many cities.
Access to Telegram, which the government has accused of being used to foment violence during the protests, was cut in the early afternoon, according to the semi-official ISNA news agency and other media.
Telecoms Minister Mohammad-Javad Azari Jahromi had accused channels on Telegram of being "counter-revolutionary" and encouraging the "use of Molotov cocktails, armed uprising and social unrest".
"If the counter-revolutionaries want to use this atmosphere to create riots, naturally the Supreme National Security Council will take action," he told the state broadcaster.
Telegram CEO Pavel Durov confirmed the blocking.
"Iranian authorities are blocking access to Telegram for the majority of Iranians after our public refusal to shut down [Sedaie Mardom] and other peacefully protesting channels," he tweeted, referring to one of the channels criticised by Iran.
Sedaie Mardom was a replacement for Amadnews, one of the biggest opposition Telegram channels with more than 1.3 million followers, which was removed after Jahromi's complaint on Saturday.
A third night of unrest in Iran saw mass demonstrations across the country, two people killed and dozens arrested.