Students gasping and coughing as they stumble out of school in ambulances. Concerned parents protest in the capital Tehran. And now a supreme leader is calling for harsh punishments for what would be an “unforgivable crime.”
The crisis over a wave of suspected poisonings that has affected thousands of schoolgirls across Iran escalated further this week, with the first arrests reported after Ayatollah Ali Khamenei made his first public comments on the matter.
Official suggestions that the mysterious incidents are a deliberate attempt to prevent girls from getting an education have led to growing public unease and questions about who or what might be behind it. They also caused global alarm in light of the unrest that has plagued the country in recent months.
NBC News looks at what we know.
How big is the crisis?
At least 2,000 people have reported symptoms, according to the latest NBC News analysis of Iran’s state and quasi-official media, though the numbers are fluid and clear reporting from Iran is difficult. However, an MP charged with investigating the incidents suggested that, while unconfirmed, the number of potential cases could be as high as 5,000.
The first cases were reported in late November in the Shiite holy city of Qom, in the heart of the Islamic Republic, according to local media, but have since spread to dozens of provinces across the country.
Details were hard to pin down — which only fueled fear in a country that had been wracked with tumult and mass unrest for months — but videos posted to social media and verified by NBC News provide a glimpse of the situation in Iran.
In one, girls cough profusely as they are escorted from school to an ambulance, while in another, a teenager drops to her knees as other students frantically try to help. It is not clear what exactly they suffer from.
State television has also broadcast images of girls struggling to breathe in hospital beds. NBC News has not verified the local reports.
No deaths have been reported, but the situation has led to growing concern among parents and even protests.
A video verified by NBC News shows a group of women protesting with placards outside a Tehran Ministry of Education building.
What have officials said?
The suspected poisonings were only recently publicly acknowledged by Iranian officials, who have offered little clue as to who or what might be behind the crisis.
Following a series of comments from government officials and reports in local media, hardline President Ebrahim Raisi said last week he had ordered an investigation into the incidents.
On Sunday, Raisi told the cabinet that the alleged incidents were “an inhumane crime” that was “designed to intimidate the students, our dear children and their parents,” according to the state-run IRNA news agency.
Iran’s Supreme Leader said on Monday that, if confirmed as deliberate, the suspected poisonings would amount to “a great and unforgivable crime”.
“The guilty must face the harshest punishment,” Ayatollah Ali Khamenei said on state television.
Iran’s Interior Minister Ahmad Vahidi said this weekend that “suspicious samples” had been collected by investigators, without elaborating. He called on the public to remain calm and accused unnamed enemies of using “media terrorism” to foment fear and undermine the country’s clerical establishment.
On Tuesday, Vahidi said that while the investigation was ongoing, “a number of responsible people involved in school disturbances” had been arrested, the semi-official ISNA news agency said. He did not name those arrested or give a possible motive.

Who could be responsible?
Many believe the Iranian government has been slow to act on the mysterious incidents that appear to threaten the education of girls in the country.
After downplaying the issue earlier, Iranian officials said last week that the suspected poisonings may have been deliberate attacks designed to prevent girls from getting an education.
“Some people wanted all schools closed, especially girls’ schools,” Iran’s deputy health minister Younes Panahi said, according to Iran’s state broadcaster IRIB.
Some have drawn parallels to previous attacks on women in Iran.
The most recent example was a spate of acid attacks around the central city of Isfahan in 2014, believed at the time to have been carried out by religious hardliners who targeted women for their clothing.
If the suspected poisonings are deliberate acts motivated by a similar motive, it would represent a major escalation in a country where girls’ education has never been seriously challenged in the four decades since the Islamic revolution.
Some prominent critics of the Iranian government have said, without providing evidence, that the recent suspected poisonings could be an act of “revenge” for the unrest that erupted across the country when 22-year-old Mahsa Amini died after being detained by the vice squad, who accused her of violating Iran’s strict dress code.
Female students were at the forefront of subsequent protests that rocked the Islamic Republic as they resisted strict dress codes by removing their headscarves and confronting officials.
“This is a government crime against children unparalleled in history.” Iranian activist and journalist Masih Alinejad tweeted Monday.
Iranian authorities have not immediately commented on the claims, but have accused “enemies” of using the attacks to undermine the regime.
The suspected poisonings led to international condemnations and calls for a thorough and open investigation, including from the United States and the United Nations.
“The possibility that girls in Iran may be poisoned simply because they are trying to get an education is shameful, it is unacceptable,” White House press secretary Karine Jean-Pierre said at a news conference Monday. She called for an independent investigation to determine whether the poisonings were related to the protests, meaning it would fall within the mandate of the UN fact-finding mission to Iran.
In a statement, the US Commission on International Religious Freedom said it was “outraged” by the reports of poisonings.
“The United States and like-minded governments must press the Iranian government to take full responsibility for stopping the poisonings and “hold the perpetrators accountable in a manner consistent with international law,” he said. committee member Sharon Kleinbaum.

What could be causing the reported symptoms?
With little clue from Iran as to what might be behind the incidents, it has been difficult to pin down the precise details of what happened.
“The biggest challenge is actually getting samples from an attack or incident like this, and getting them properly verified,” said Hamish de Bretton-Gordon, a former commander of the United Kingdom’s chemical, biological and nuclear forces and NATO.
However, given strained relations with the West, “Iran does not seem eager to reveal this incident to the world. And it seems highly unlikely that they will ask the UN to help with the investigation, he told NBC News.
Some Iranian officials have said nitrogen gas appeared during testing at affected schools, while reported symptoms ranged from headaches and dizziness to girls feeling palpitations and pain in their legs.
“It could be something like sulfur dioxide, a toxic industrial chemical used in various industrial processes. It has also been suggested that it could be nitrogen dioxide,” de Bretton-Gordon said of the possible cause. But those chemicals “are usually stored in some kind of steel containers in liquid or gaseous form. So simply opening the guts of those cylinders would spread it over a relatively large area,” he said.
Taking blood samples from affected girls may offer the best hope for answers, he said, but beyond that, conclusions may prove elusive. “If you’re looking for environmental samples, in the dust, in the dirt or in the concrete, that can be very volatile, especially in a place where it’s hot,” de Bretton-Gordon added.
But what if most reported cases contain no chemicals at all?
Iranian state media has sometimes referred to the spate of cases as “hysterical reactions” among the schoolgirls, hinting at another possibility that some experts say is at least playing a role in the crisis – especially given the context of the government’s crackdown to the nationwide protests and the absence of many boys reporting similar symptoms.
Deputy Health Minister Saeed Karimi said on Monday that some students had been exposed to “a stimulant material by inhalation,” according to the semi-official Tasnim news agency, but said it likely affected less than 10% of cases under investigation. Others suffered from anxiety or stress, he said.
The news agency also reported that the Interior Ministry said less than 5% had been exposed to “stimulant chemicals” and others had reported symptoms “due to anxiety and stress”.
NBC News has not independently verified those numbers.
A similar phenomenon was reported in Afghanistan from 2009 to 2012, with hundreds of girls across the country complaining of strange odors and poisoning, according to the Associated Press.
No evidence was found to support the suspicions, and the World Health Organization said it resembled “mass psychogenic illness”.