Hundreds of protesters took to the streets of a north-western Iranian city on Wednesday to mark 40 days since the death in custody of 22-year-old Mahsa Amini, which sparked the country’s biggest anti-government movement in more than a decade.

Deaths are commemorated in Shiite Islam – as in many other traditions – again 40 days later, typically with an outpouring of grief.

In Ms Amini’s Kurdish hometown of Saqez, the birthplace of the nationwide unrest, crowds snaked through the local cemetery and thronged her grave.

“Death to the dictator!” protesters cried.

State-run media announced that schools and universities in north-western Iran would close, purportedly to curb “the spread of influenza”.

In central Tehran, shops were shuttered and riot police were out in force.

A group of schoolgirls marched through the streets, shouting against the government as cars stuck in traffic honked their support, witnesses said.

Anti-government chants also echoed from the University of Tehran campus.

Ms Amini, detained by Iran’s morality police for allegedly violating the country’s strict dress code for women, remains the potent symbol of protests that have posed one of the most serious challenges to the Islamic Republic.

With the slogan #WomanLifeFreedom, the demonstrations first focused on women’s rights and the state-mandated hijab, or headscarf for women. But they quickly evolved into calls to oust the Shiite clerics that have ruled Iran since the 1979 Islamic Revolution.

The protests have also galvanised university students, labour unions, prisoners and ethnic minorities like the Kurds along Iran’s border with Iraq.

Since the protests erupted, security forces have fired live ammunition and tear gas to disperse demonstrations, killing more than 200 people, according to rights groups.

Untold numbers have been arrested, with estimates in the thousands.

Iranian judicial officials announced this week that they would put more than 600 people on trial for their role in the protests, including 315 in Tehran, 201 in the neighbouring Alborz province and 105 in the south-western province of Khuzestan.

Tehran prosecutor Ali Salehi told the state-run Irna news agency that four protesters have been charged with “war against God”, which is punishable by death in Iran.

Iranian officials have blamed the protests on foreign interference, without offering evidence.