Iran must deal decisively with protests that swept the country after the death in custody of a woman detained by the Islamic Republic's morality police.
President Ebrahim Raisi said on Saturday.
Thirty-five people have been killed in the weeklong demonstrations, according to Iran's state television, with the protest spreading to most of the country's 31 provinces.
On Friday, state-organised rallies took place in several Iranian cities to counter the anti-government protests, and the army promised to confront "the enemies" behind the unrest.
State media quoted Raisi on Saturday as saying Iran must "deal decisively with those who oppose the country's security and tranquillity".
Raisi was speaking by telephone to the family of a member of the Basij volunteer force killed while taking part in the crackdown on unrest in the northeastern city of Mashhad.
The president "stressed the necessity to distinguish between protest and disturbing public order and security, and called the events ... a riot," state media reported.
The protests broke out in northwestern Iran a week ago at the funeral of Mahsa Amini, a 22-year-old Kurdish woman who died after falling into a coma following her detention by morality police enforcing hijab rules on women's dress.
Her death has reignited anger over issues including restrictions on personal freedoms in Iran, the strict dress codes for women and an economy reeling from sanctions.
Women have played a prominent role in the protests, waving and burning their veils. Some have publicly cut their hair as furious crowds called for the fall of Supreme Leader Ayatollah Ali Khamenei.
The protests are the largest to sweep the country since demonstrations over fuel prices in 2019 when Reuters reported 1,500 people were killed in a crackdown on protesters. It was the bloodiest confrontation in the Islamic Republic's history.
Iranian news agencies reported on Saturday that 739 protesters had been arrested in the northern province of Gilan, on the Caspian Sea.
The activist Twitter account 1500tasvir, which has 125,000 followers, said communication channels with the northwestern town of Oshnavieh had been cut off, and landlines were down.
Oshnavieh was one of several towns in northwest Iran, where most of the country's 10 million Kurds live, that held a strike on Friday.