Iranian officials acknowledged on Sunday that girls at more than 50 schools were victims of poisonings.
Fear about the poisonings has spread among parents after months of unrest in the country.
The poisonings began in November in the holy city of Qom and it remains unclear who or what is responsible.
Reports now suggest schools across 21 of Iran's 30 provinces have had suspected cases, with girls' schools the site of nearly all incidents.
The attacks have raised fears that other girls could be poisoned, apparently just for going to school.
Education for girls has never been challenged at any time since the 1979 Islamic Revolution.
Iran has been calling on the Taliban in neighbouring Afghanistan to allow girls and women return to school and universities.
Protests in Iran - in pictures
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Iranians protest in Tehran after the death of 22-year-old Mahsa Amini after she was detained by the morality police in September. AP Photo -
Protests have intensified despite a vicious government crackdown that has left as many as 200 people dead, although estimates of the toll by rights groups vary. AP Photo -
At least eight members of the security forces have also been killed or wounded during the unrest and there are signs that violent resistance could be intensifying. AP Photo -
A fire burns at the office of the governor of Mahabad, in the West Azerbaijan province of Iran. AFP -
Protesters gather in the a courtyard of Chitgar complex in western Tehran. AFP -
Iranian protesters continue to defy a deadly crackdown by security forces. AFP -
A woman cuts her hair at the grave site of Nika Shahkarami in the city of Khorramabad, during a reported memorial held to mark 40 days since the death of the 16-year-old. AFP -
A woman not wearing a headscarf stands on top of a vehicle as thousands make their way towards Saqez, Mahsa Amini's home town, to mark 40 days since her death in police custody. AFP -
Iranian riot police prepare to confront protesters the capital, Tehran. AFP -
Iranian protesters surge forward amid clashes with riot police in Tehran. AFP -
A crowd blocks an intersection during a protest to mark 40 days since Amini's death in custody. AP Photo -
Iranian police arrive to disperse a protest in Tehran. AP Photo -
Protesters chant at a vigil for Amini at the Khajeh Nasir Toosi University of Technology in Tehran. Reuters -
Students at Sharif University of Technology attend a protest. AP Photo -
Police outside Sharif University during a student protest. AP Photo -
Students at the university protest over the death of Amini, who was in 'morality police' custody for allegedly breaking strict rules on head coverings for women. AP Photo -
The students' banner says: 'No to mandatory hijab'. AP Photo
Interior Minister Ahmad Vahidi on Saturday said that investigators recovered “suspicious samples” in the course of their investigations into the incidents, the state-run Irna news agency said.
Mr Vahidi called for calm among the public, while also accusing the “enemy’s media terrorism” of inciting more panic over the poisonings.
But it was not until the poisonings received international media attention that hard-line President Ebrahim Raisi announced an investigation into the incidents on Wednesday.
On Sunday, Mr Raisi told the Cabinet, following a report read by Intelligence Minister Ismail Khatib, that the cause of the poisonings must be uncovered and confronted.
He described the attacks as a “crime against humanity for creating anxiety among student and parents".
Mr Vahidi said at least 52 schools had been affected by poisonings.
Iranian media reports have put the number of schools at more than 60. At least one boy's school has reportedly been affected.
Iranian-American celebrities show support for protest movement in Iran - in pictures
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Sarah Shahi, who was born in the US to Iranian parents, has been vocal in her support of the protests. Pictured in London this week to promote the 'Black Adam' film. Photo: Warner Bros -
Shahi at a 'Black Adam' premiere in London on Tuesday. Photo: Warner Bros. -
Yara Shahidi has repeatedly drawn attention to the situation in Iran on her Instagram account, where she has more than 7 million followers. AFP -
US actress Yara Shahidi, pictured in 2017. EPA -
Navid Negahban, who was born in Iran, has posted support in both Farsi and English. Fatima Al Marzooqi / The National -
Negahban in between takes while filming a scene during the shooting of the short film '51' at the Central Souk in Abu Dhabi on June 28, 2013. Christopher Pike / The National -
Maz Jobrani, a veteran Iranian-American comedian, recently posted a video on Instagram imploring people to care about what is happening in Iran. Photo: Levity Entertainment
Videos of upset parents and schoolgirls in emergency rooms with intravenous drips in their arms have flooded social media.
Making sense of the crisis remains challenging, given that nearly 100 journalists have been detained by Iran since the start of protests in September over the death of Mahsa Amini, 22.
Ms Amini had been detained by the country's morality police and later died.
The security force crackdown on those protests has led to at least 530 people killed and 19,700 detained, according to Human Rights Activists in Iran.
The children affected in the poisonings reportedly complained of headaches, heart palpitations, or feeling lethargic or unable to move.
Some described smelling tangerines, chlorine or cleaning agents.
Reports suggest at least 400 schoolchildren have fallen ill since November. Mr Vahidi said two girls remain in hospital because of underlying chronic conditions.
As more attacks were reported on Sunday, videos were posted on social media showing children complaining about pain in the legs and abdomen, and dizziness.
State media have mainly referred to these as “hysteric reactions".
Mahsa Amini protests in Iran and around the world - in pictures
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Demonstrators chant slogans during the March of Solidarity for Iran in Washington. AFP -
Another group of demonstrators at the march. AFP -
A protest in support of Iranian women in Barcelona. Reuters -
Iranian citizens and locals joined in the Barcelona protest. Reuters -
People attend a demonstration in solidarity with Mahsa Amini and other Iranian women in Castello Square, Turin. EPA -
A person places a candle during the demonstration in Turin. EPA -
A protester holds a pre-Islamic Revolution Iranian flag during a demonstration in Brussels in support of the Iranians fighting for their freedom. AFP -
A protester wearing a top with a logo that reads 'No to an Islamic state" as she takes part in a rally in support of the Iranian people, in Brussels. AFP -
People wave the Shah-era Iranian flag during a protest in Paris. AFP -
A woman shows her true colours in the protest against the Iranian government, in Paris. AFP -
A woman holds a flag, as people protest against the Iranian regime outside Iran's embassy in central London. Reuters -
Supporters of the Kurdistan Workers' Party (PKK) carry placards and wave party flags in Beirut, during a protest against the death of Ms Amini. EPA -
People demonstrate against the Iranian government outside the Houses of Parliament in London following the death of Amini. Reuters -
A mural in Paris depicts women cutting their hair to show support for Iranian protesters. AP -
People take part in a rally against the Iranian government in Vancouver, Canada, on Saturday. AP -
Protesters take to the streets of Tehran. EPA -
Iranian protesters run after clashing with with police. EPA -
A protester shaves their head outside the Houses of Parliament in London. Reuters -
Iranians living in Athens hold a protest in solidarity. AFP -
People take part in a rally in The Hague. AFP -
A woman cuts her hair during a demonstration in Santiago, Chile, by feminist groups and Iranian migrants in support of Iranian women following the death of Amini. AFP -
Members of feminist groups and Iranian migrants during the protests in Santiago. AFP -
Iranian activists shout slogans during a protest against the government in Tehran, in Amsterdam, The Netherlands. EPA -
A protester holds a painted portrait of Mahsa Amini in Berlin, Germany. EPA -
A protester shows red paint on her face, resembling blood splatters and bloody handprints next to the national Iranian emblem, during a rally in Berlin. EPA -
Iranian protesters shout slogan during a protest in Istanbul, Turkey. EPA -
A woman holds a sign during a protest against the Iranian government, in front of the country's embassy in Madrid, Spain. The protests were triggered by the death of a young Iranian woman, Mahsa Amini, in police custody. Reuters -
A woman cuts her hair during the protest in front of the Iranian embassy in Madrid. Reuters -
Israelis show their support for women in Iran as they hold up placards of Amini during a protest in Jerusalem. EPA -
Amini, 22, was arrested in Tehran on September 13, 2022, by the morality police. She fell into a coma while in police custody and was declared dead on September 16. EPA -
People walk by graffiti in support of the protests triggered by Amini's death, in Jerusalem. EPA -
A protest in Nantes, western France, after the death of Amini in Iranian police custody. AFP -
Women gather for a demonstration in Barcelona, Spain. AFP -
Demonstrators in Nantes. Amini's death has sparked a global protest movement. AFP -
Women protest outside the town hall in in Montpellier, southern France. AFP -
A woman at a protest in Catalunya Square, Barcelona. Reuters -
Campaigners and football fans protest at a Champions League match between Porto and Bayer Leverkusen at the Dragao stadium in Portugal. EPA -
People hold placards during a demonstration in solidarity with the Iranian people near the European Parliament in Strasbourg, France. EPA -
An Iranian woman living in Turkey with 'Freedom' written on her forehead takes part in a protest near the Iranian consulate in Istanbul. Reuters -
In Barcelona, protesters take part in a demonstration in support of Iranian women. AFP -
A Lebanese activist takes part in a protest in Beirut, triggered by the death of Amini, 22. AP -
A Turkish protester takes off her head scarf while giving a performance in Instanbul during a protest against Iran over Amini's death. Getty -
A woman in Istanbul cuts her hair during a protest against Iran. Getty -
A Lebanese activist holds a poster depicting Amini during a protest in Beirut organised by feminist groups in support of women protesters in Iran. EPA -
Demonstrators in Los Angeles, California, hold the Iranian flag during a protest against the government in Tehran. AFP -
Demonstrators hold placards in Mexico City during a protest against Iran. Reuters -
People demonstrate in Montreal, Canada, during a protest triggered by Amini's death. AFP -
Iranian Americans participate in a rally in central Los Angeles, in solidarity with women in Iran. AP -
Demonstrators march during a protest in Los Angeles, California. AFP -
A woman with the colours of the Iranian flag painted on her face participates in a rally as thousands demonstrate in support of Iranian women in Los Angeles. EPA -
Australians protest over Amini's death in Melbourne. EPA -
Police block protesters from entering Iran's embassy in Oslo, Norway. EPA -
Demonstrators in front of the European headquarters of the UN in Geneva, Switzerland, during a rally against Iran. EPA -
A candlelight vigil for Amini in Los Angeles. AFP -
Afghan women hold placards as they take part in a protest in front of the Iranian embassy in Kabul. AFP -
Protestors take part in a rally outside the Iranian consulate in Istanbul. AFP -
An Iranian woman shows a lock of hair she cut off during a protest outside the Iranian consulate in Istanbul. EPA -
Demonstrators outside the Iranian consulate in Istanbul. Getty -
Iranian Americans rally on Capitol Hill in Washington to show support for protesters in Iran. AFP -
Protesters on Capitol Hill hold a sign condemning the crackdown by Tehran. AFP -
German demonstrators gather in Berlin after the death of Amini in Iranian police custody. AP -
A protester cries during a rally in Berlin. Reuters -
A demonstration in Madrid, Spain. Thousands have gathered in cities across Europe to support protests in Iran. AP -
Demonstrators gather outside the Iranian embassy in Madrid. Reuters -
People take part in a protest in Lausanne, Switzerland. EPA -
Protesters hold signs featuring images of Amini during the protest in the western Swiss city. EPA -
Demonstrators in front of the Iranian embassy in Buenos Aires, Argentina. EPA -
An activist outside the Iranian embassy in Buenos Aires, Argentina, with a sign that reads 'Justice for Mahsa Amini'. AFP -
A demonstration against violence in Iran is held in Quito, Ecuador. The Iranian community in Ecuador protested outside the Iranian embassy. EPA -
Protesters at a demonstration outside the Iranian embassy in Quito, Ecuador. EPA
Since the outbreak, no one was reported in critical condition and there have been no reports of deaths.
Attacks on women have happened in the past in Iran, most recently with a wave of acid attacks in 2014 around the city of Isfahan, at the time believed to have been carried out by hard-liners attacking women for how they dressed.
Speculation in Iran's tightly controlled state media has focused on the possibility of exile groups or foreign powers being behind the poisonings.
That was also repeatedly claimed during the recent protests, without evidence.
In recent days, Germany's Foreign Minister Annalena Baerbock, a White House official and others have called on Iran to do more to protect schoolgirls, which Iran's Foreign Ministry has dismissed as “crocodile tears".
But the US Commission on International Religious Freedom said Iran had “continued to tolerate attacks against women and girls for months” amid the recent protests.
"These poisonings are occurring in an environment where Iranian officials have impunity for the harassment, assault, rape, torture and execution of women peacefully asserting their freedom of religion or belief,” the commission's Sharon Kleinbaum said.
Suspicion in Iran over the poisonings has fallen on hard-liners.
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Iranian journalists, including Jamileh Kadivar, a prominent former reformist politician at Tehran’s Ettelaat newspaper, have quoted a supposed communique from a group calling itself Fidayeen Velayat.
It reportedly said that girls' education "is considered forbidden" and threatened to “spread the poisoning of girls throughout Iran” if girls’ schools remain open.
Iranian officials have not acknowledged any group called Fidayeen Velayat, which roughly translates to English as “Devotees of the Guardianship.”
But Ms Kadivar’s mention of the threat in print comes as she remains influential within Iranian politics and has ties to its theocratic ruling class.
The head of the Ettelaat newspaper also is appointed by Supreme Leader Ayatollah Ali Khamenei.
Ms Kadivar wrote Saturday that another possibility is “mass hysteria."
There have been previous cases of this over the last decades, most recently in Afghanistan from 2009 through 2012.
Then, the World Health Organisation wrote about so-called “mass psychogenic illnesses” affecting hundreds of girls in schools across the country.
"Reports of stench smells preceding the appearance of symptoms have given credit to the theory of mass poisoning," WHO wrote at the time.
"However, investigations into the causes of these outbreaks have yielded no such evidence so far."
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Iran has not acknowledged asking the world health body for assistance in its investigation.
WHO did not immediately respond to a request for comment Sunday.
But Ms Kadivar also noted that hard-liners in Iranian governments in the past carried out “chain murders" of activists and others in the 1990s.
She also referred to the killings by Islamist vigilantes in 2002 in the city of Kerman, when one victim was stoned to death and others were tied up and thrown into a swimming pool, where they drowned.
Ms Kadivar described those vigilantes as members of the Basij, an all-volunteer force in Iran's paramilitary Islamic Revolutionary Guard Corps.
“The common denominator of all of them is their extreme thinking, intellectual stagnation and rigid religious view that allowed them to have committed such violent actions,” she wrote.
