Iranian President Ebrahim Raisi addresses lawmakers while defending his next year s budget bill at the parliament in Tehran, Iran, Sunday, Jan. 22, 2023. AP
The president's website said Ebrahim Raisi had assigned Interior Minister Ahmad Vahidi to provide "continuous information on the results of the investigation" into the attacks.
Hundreds of cases of respiratory distress have been reported in the past three months among schoolgirls in what one government official said could be an attempt to force the closure of girls' schools in the Islamic republic.
At least 10 girls' schools were targeted in the latest suspected attacks on Wednesday, seven in the northwestern city of Ardabil and three in the capital, media reports said.
The incidents in Ardabil forced the hospitalisation of 108 students, all of whom were in stable condition, said Tasnim news agency, which also reported poisonings at three schools in Tehran.
Citing parents, Fars news agency said students at one high school in the capital's western neighbourhood of Tehransar had been exposed to a toxic spray. It did not elaborate.
President Raisi's website said he had appointed Vahidi in an effort to "allay the concerns of the families" of the students affected.
Vahidi held a press conference at which he debunked earlier reports from Fars on Wednesday that security forces had detained three people in the first reported arrests over the wave of suspected poisonings.
"There are various reports that are completely false," he told journalists, also saying that reports of the detection of a specific chemical substance being used in attacks were incorrect.
Parliament's website had said health ministry tests on a substance found at the schools in the holy city of Qom, where 800 students were affected, had detected traces of nitrogen, which is mainly used in fertilisers.
Since the outbreak of the mysterious poisonings in November, almost 1,200 students have required hospital treatment for breathing difficulties, a lawmaker said Wednesday.
Apart from Qom south of Tehran, 400 were affected in the western city of Borujerd, said Zahra Sheikhi, spokesperson for parliament's health committee.
The poisonings have provoked a wave of anger across the country, with critics denouncing official silence in the face of the growing number of schools reportedly being targeted.
On Sunday the deputy health minister, Younes Panahi, said some people had been poisoned in Qom with the aim of shutting down education for girls.
Activists have compared those responsible for the attacks on schools to the Taliban in Afghanistan and Boko Haram in the Sahel, groups which oppose education for girls.