The anti-government protests that have erupted in cities across Iran in response to a young woman's death in the custody of the country's morality police have struck a national nerve.

The demonstrations have spread to dozens of cities, and multiple casualties have been reported. The government said on Thursday that 17 people, including two security officers, had been killed since the unrest began last weekend. Rights groups say the toll is likely to be higher.

The protests have included large numbers of women, who initially took to the streets in rare displays of defiance of the government and its enforcement of the country's hijab law, which mandates covered hair and loose-fitting clothing for women.

The demonstrations have become widespread, with demands broadening to reflect ordinary Iranians' anger over their living conditions after years of US-led sanctions that have hobbled the economy, as well as widespread corruption and economic mismanagement.

With extraordinary scenes of dissent and calls to end the Islamic Republic, the protests have become one of the most visible challenges to the government since the last wave of unrest in 2019, which was met with a deadly response.

Authorities have struck back again with a brutal and systematic crackdown: Security forces have fired on protesters with gunshots and water cannons and beat them with batons. Cellphone and internet usage has been dramatically restricted.

What's fueling the protests? And what are the implications for authorities?

A young woman's death ignited long-simmering anger.

Ms Mahsa Amini, who also went by the name Jina, was with her family last week on a visit to Teheran from her home in the north-western province of Kurdistan when she was arrested on an accusation of violating the hijab law.

The law came into effect in 1981, after the Islamic Revolution. It has long been challenged by many women in Iran, and is commonly flouted across the country.

Ms Amini, 22, died three days after her detention while in the custody of the morality police, who enforce the country's strict Islamic rules.

Iran's security forces issued a statement saying that Ms Amini had collapsed from a heart attack at the detention centre while receiving training on hijab rules. Her family disputed this claim, saying she was perfectly healthy before her arrest, according to news reports.

Her death quickly struck a national nerve and gave a human face to the public's long-simmering anger over the religious laws.

Many women ripped off and burned their head coverings to protest the hijab law, videos posted to social media and by the BBC's Persian service showed, even in the conservative and religious city of Mashhad in the north-east.

One widely circulated video, from the city of Kerman, in the south-east, showed a woman cutting her hair in front of a roaring crowd.

As anger gripped the country, more and more Iranians have joined the demonstrations, turning the crisis into an outlet for broader frustrations with the government.

Many have called for a scrapping of the far-reaching religious restrictions, which govern how people dress, how they socialise in their homes and what they drink and eat.

Even some conservatives have taken up that call, arguing that criminalising violation of the rules and imposing them by force has backfired and fuelled resentment towards religion.

Analysts also say that years of economic decline have stretched the patience of many Iranians, who have periodically taken to the streets in protest in recent years.

Iran's economy has been at rock bottom for years. US-led sanctions in response to the country's nuclear and missile programmes have made it much harder for Iran to sell its oil and cut access to the global financial system, and corruption and economic mismanagement are rife.

Iranians have long been subject to ever-rising inflation, food shortages and supply disruptions, and a scarcity of jobs.

Authorities are answering with practised force

Many embittered Iranians have directed their hostilities towards the heart of the country's system of government: the supreme leader Ayatollah Ali Khamenei.

Footage showing protesters chanting for his death and the downfall of his son Mojtaba, seen as a potential successor, have coursed through social media.

In the northern city of Rasht, protesters took over a street, chanting: "Death to the dictator!" and "Death to the oppressor, be it the shah or the supreme leader!"

The government has struck back with a brutal and systematic crackdown, using well-rehearsed tactics seen in previous anti-government uprisings. Videos on social media show protesters facing off against large deployments of riot police officers, who have targeted them with gunshots and water cannons and beat them with batons. Plainclothes officers from the feared Basij militia have also been sent against the protests.

In the north-western province of Kurdistan alone, at least 17 protesters have been killed, according to the Kurdistan Human Rights Network, which has posted names and photos of the victims online.

At least 733 people have been injured and more than 600 people arrested across the Kurdish province, according to Hengaw, another rights group.

The figures issued by the government did not include details of where casualties had occurred.

The protests have showed no signs of easing.

On Thursday, the Revolutionary Guard, Iran's powerful security force, issued a statement describing what was occurring as sedition and saying that protesters must be crushed to teach other people a lesson.

Since the start of the protests, the government has significantly curbed the three main operators providing mobile internet service, severely disrupted internet in areas where protests are taking place and blocked platforms such as WhatsApp and Instagram, according to NetBlocks, an internet watchdog, and Iranian digital experts. Protesters had been making heavy use of those platforms to galvanise support and track unfolding events.

In Teheran, power was cut at night, casting the streets into total darkness in some of the central and downtown neighborhoods where protests had been more intense, according to several residents.

Iranian women have long fought for their rights, and been punished for it. This is not the first time the theocracy at the helm of the Iranian government has cracked down on women protesting for greater rights.

Iranian women have been challenging the hijab rule since its inception in 1981 and testing the limits of what they could get away with. As younger generations of women came of age, they became bolder in removing headscarves in public and calling for an end to mandatory hijabs.

It's part of a wider push among Iranian women on issues such as divorce, child custody and the right to work and travel without a male guardian's approval and against other discriminatory laws.

In 2017, a 31-year-old mother, Ms Vida Movahed, stood on a utility box in downtown Tehran, removed her hijab and waved it before a crowd on a stick. More women started to follow her lead, giving way to the so-called Girls of Revolution Street protest, which was later quashed by the government.

In 2019, a 29-year-old woman named Ms Sahar Khodayari set herself on fire after she was arrested for sneaking into a men's football match.

The Iranian government, under pressure from international football authorities, later changed the law and allowed women to attend matches, but they were relegated to cordoned-off areas.

That same year, Ms Nasrin Sotoudeh, a prominent Iranian lawyer who defended women who removed their headscarves, was sentenced to 38 years in prison and 148 lashes on charges of "colluding against the system" and "insulting" leader Khamenei.

Previous protests were stamped out with beatings, arrests and close-range gunfire.

The current demonstrations are the most dramatic displays of dissent that the country has seen since November 2019, when a rise in gas prices touched off the most sweeping and violent riots since the revolution. Many of those on the streets protesting were lower-income people particularly hard hit by the changes.

Iran shut down the Internet for several days, and security forces opened fire on protesters, often from close range, quashing the widespread demonstrations in a matter of days. Rights groups say at least 360 people were killed in the brutal crackdown, but other estimates were much higher.

A previous round of protests, the so-called Green Movement, that swept the country in 2009 had been led by the middle class and university students, who turned out on the streets to denounce the fraudulent re-election of the conservative president at the time, Mr Mahmoud Ahmadinejad. Then, too, authorities also cracked down hard, with the Revolutionary Guard and the Basij sent in to arrest, beat and kill protesters.

Ms Neda Agha Soltan, a young woman who was shot and killed, became the symbol of the uprising. NYTIMES