Anti-government demonstrations that began in one city on Thursday have now spread to several major cities in Iran.
Large numbers are reported to have turned out in Rasht, in the north, and Kermanshar, in the west, with smaller protests in Shiraz, Isfahan and Hamadan.
The protests began against rising prices but have spiralled into a general outcry against clerical rule.
A small number of people have been arrested in Tehran, the capital.
They were among a group of 50 people who gathered in a city square, Tehran's deputy governor-general for security affairs told the Iranian Labour News Agency.
The governor-general of Tehran earlier said that any such gatherings would be firmly dealt with by the police, who are out in force on main intersections.
The demonstrations are the most serious and widespread expression of public discontent in Iran since protests in 2009 that followed a disputed election, correspondents say.
Demonstrators were reportedly heard yelling "The people are begging, the clerics act like God".
The biggest protest on Thursday was in the north-eastern city of Mashhad, where there were 52 arrests.
There have been calls on social media for protests up and down the country, despite warnings from the government against illegal gatherings.
Videos posted on social media purport to show clashes between security forces and some demonstrators in Kermanshah on Friday.
The protests on Thursday started with anger at the inability of the government of President Hassan Rouhani to control prices – the cost of eggs has doubled in a week.
However, some developed into broader anti-government protests, calling for the release of political prisoners and an end to police beatings.
There were also chants in Mashhad of "not Gaza, not Lebanon, my life for Iran", a reference to what protesters say is the administration's focus on foreign policy rather than domestic issues.
The arrests in Mashhad were for chanting "harsh slogans", officials said.
Analysis by Kasra Naji, BBC Persian
The demonstrations have taken the Iranian authorities by surprise. Impromptu anti-government demonstrations are rare in a country where the Revolutionary Guard and numerous intelligence agencies have a strong grip on the population.
Predictably they are blaming anti-revolutionary elements and foreign agents. But the protests clearly stem from seething discontent in Iran, mainly because of the worsening economic conditions faced by ordinary Iranians.
A BBC Persian investigation has found that Iranians, on average, have become 30% poorer in the past ten years alone.
Many believe that money that should be used to improve their lives is being spent by Iran's leaders on conflicts in Syria, Yemen and Iraq. Billions are also being spent on spreading religious propaganda and Shia Islam around the world.
But it seems that the hardliners opposed to President Rouhani may have triggered the unrest by holding a demonstration that quickly grew out of control and spread to cities and towns across the country.
The head of Mashhad's revolutionary court, Hossein Heidari, said: "We consider protest to be the people's right but if some people want to abuse these emotions and ride this wave, we won't wait and will confront them."
President Rouhani promised that the deal he signed with world powers in 2015, which saw Iran limit its nuclear activities in return for the lifting of international sanctions, would boost economic growth.
The economy has risen out of recession and inflation has been reduced, but businesses are still struggling from a lack of investment and the official unemployment rate is 12.4%.