Iran's President Ebrahim Raisi on Wednesday ordered authorities to investigate incidents in which noxious fumes have made pupils sick at girls' schools, which some officials suspect are attacks on women's education.
Since November, hundreds of girls at about 30 schools have been made ill, with some being admitted to hospital.
Iranian officials initially dismissed the incidents, only acknowledging the scope of the crisis in recent days.
Girls have complained about headaches, heart palpitations, feeling lethargic or otherwise unable to move.
Some described smelling tangerines, chlorine or cleaning agents.
Unlike neighbouring Afghanistan, Iran has no history of religious extremists attacking girls' education.
Women and girls continued attending school even at the height of the 1979 Islamic Revolution that toppled Iran's western-backed shah.
Iran protests 40 days since Mahsa Amini's death - in pictures
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An unveiled woman stands on top of a vehicle as thousands make their way towards Aichi cemetery in Saqez, Mahsa Amini's home town, to mark 40 days since her death. AFP -
Protesters attempt to dodge projectiles fired at them during clashes at Iran's Islamic Azad University in Tehran. AFP -
Protesters gather at Amirkabir University of Technology in Tehran. AFP -
A man, bottom left, fires a weapon during the clashes at Islamic Azad University. AFP -
Protesters chant at a vigil for Amini at the entrance of the Khajeh Nasir Toosi University of Technology in Tehran. Reuters -
Iranian police arrive to disperse a protest marking 40 days since Amini's death. AP -
People block an intersection during a protest to mark 40 days since Amini's death. AP -
People march down the motorway towards Aichi cemetery near Saqez, where Amini is buried. Reuters -
People march towards Aichi cemetary. Reuters -
Protesters walk towards the cemetery. Reuters -
A view of demonstrators walking to the cemetery. Reuters -
Cars line the street as people march towards the cemetery. Reuters -
Protesters march towards the cemetery 40 days after Amini's death. Reuters
At a Cabinet meeting on Wednesday, Mr Raisi said the Interior Ministry should investigate the incidents, with help from the health and intelligence ministries, and promptly release the results to the public, the state-run Irna news agency reported.
It was the first time he has publicly addressed the poisonings.
The night before the Cabinet meeting, a senior security official played down the matter, dismissing it as psychological warfare by unnamed enemies of the country.
“Over 99 per cent of this is caused by stress, rumour and psychological war started particularly by hostile TV channels, to create a troubled and stressful situation for students and their parents,” deputy interior minister Majid Mirahmadi told state TV.
“Their goal was to force schools to close.”
The latest Iranian protests around the world - in pictures
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Last month's death in custody of Kurdish-Iranian woman Mahsa Amini has led to protests across Iran. In Brussels, Belgium, people took to the streets in sympathy to call for freedom and democracy in Iran as a two-day meeting of European Council leaders was in session. EPA -
Demonstrators in Brussels, Belgium, raise their voices against the Iranian government. Reuters -
People gather in solidarity with protesters in Iran outside the State Library of Victoria in Melbourne, Australia. EPA -
People gather for a rally in solidarity with protesters in Iran, outside the State Library of Victoria in Melbourne, Australia. EPA -
Demonstrators on the streets of the south-eastern Iranian city of Zahedan continues their resistance after Mahsa Amini died on September 16, following her arrest by the morality police in Tehran for failing to observe the state's dress code for women. AFP -
In defiance of Iranian headscarf laws, women offer hugs to passers by on a street in the Ekbatan Town in Tehran. A sign on the wall behind them reads: "Hugs for those who are sorrowful". AFP -
Iranian climber Elnaz Rekabi arrives at the Imam Khomeini International Airport in Tehran after competing in South Korea without wearing a mandatory headscarf. Rekabi said the act was unintentional as she rushed to prepare for competition and apologised. EPA -
A welcome at Imam Khomeini International Airport in Tehran for climber Elnaz Rekabi, who competed in South Korea without a hijab. AFP -
A rally in support of Iranian climber Elnaz Rekabi outside the Iranian embassy in Seoul, South Korea, after she was criticised for competing without a hijab. AP -
Protesters cut their hair and shout slogans during a rally to support Iranian competitive climber Elnaz Rekabi, outside the Iranian Embassy in Seoul, South Korea. AP -
A demonstrator outside the embassy of Iran in Jakarta, Indonesia, protests against the death in police custody of Mahsa Amini. Reuters -
Outside the embassy of Iran in Jakarta, Indonesia, a woman cuts her hair during a protest against the Iranian government the death of Mahsa Amini. Reuters -
Demonstrators take part in a protest against the Iranian government outside the embassy of Iran in Jakarta, Indonesia. Reuters
The poisonings come at a sensitive time for Iran, which has faced months of nationwide protests since a young woman died in September after being arrested by the morality police for wearing her hijab "inappropriately".
After months of playing down the poisonings, Irna filed stories on the subject on Sunday, in which officials acknowledged the scope of the incidents.
Iran’s prosecutor general has ordered an investigation, saying: “There are possibilities of deliberate criminal acts.”
It quoted a deputy health minister as saying that unnamed people wanted the schools to close.
Suspected extremists attacked women with acid for not dressing conservatively enough around the Iranian city of Isfahan in 2014.
But there is no opposition to women's education in Islam, and Iran has even called on the Taliban in Afghanistan to let women and girls return to school.
