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.
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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.”
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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.