Iran's president recently ordered an investigation into a series of sicknesses from poisonous air at a number of girls' schools in the country.
Some officials suspect the incidents are attacks targeting women's education.
Hundreds of girls at about 30 schools have been sickened since November, with some needing hospital care.
Children have reported head pain, fast heartbeats, feeling tired or weakened.
Some described sensing a smell of the fruit tangerine, chlorine and chemicals used in cleaning.
On Wednesday, Iranian President Ebrahim Raisi told a Cabinet meeting that the Interior Ministry should investigate the incidents.
He said the country's health and intelligence ministries should help in the investigation.
It was the first time Raisi had spoken publicly about the sicknesses.
A day earlier, a top security official had dismissed the reports of possible poisonings.
The Interior Ministry official, Majid Mirahmadi, called the reports "psychological warring" by enemies in media and elsewhere.
"Their goal was to force schools to close," he said.
The first cases of sickness happened late last year in Qom, a city some 125 kilometers southwest of Iran's capital, Tehran.
The city is known for its conservative religious history.
Students at Qom's Noor Yazdanshahr Conservatory got sick in November.
They recovered before becoming sick again the next month.
Then other cases, at other girls' schools, followed.
At first, officials did not connect the cases at different schools.
Some questioned if the natural gas systems that heated schools was to blame.
But the sicknesses were happening only at schools for females.
Since then, officials say at least one boys' school has been targeted as well.
Ali Reza Monadi is a national parliament member who sits on its education committee.
He described the poisonings as "intentional."
"We have to try to find roots," of the incidents, he told Iran's state media agency, IRNA.
Shargh, a reformist news website based in Tehran, reported that many parents have withdrawn their students from school.
On Tuesday, another suspected attack was reported at a girls' school in Pardis on the eastern outskirts of Tehran.
The poisonings come as getting confirmable information out of Iran remains difficult.
The government is strongly punishing any public show of dissent following months of huge civil rights demonstrations in the country.
Security forces have arrested at least 95 press workers since protests broke out in September of last year, reports the New York-based Committee to Protect Journalists.
Human rights activists in Iran say at least 530 people have been killed in the increased security measures.
They say Iranian security forces have arrested about 19,700 people as well.
Attacks on women have happened in the past in Iran, most recently with a wave of acid attacks in 2014 around Isfahan.
At the time, the attacks were believed to have been carried out by religious extremists targeting women for the clothing they wore.
But, even in the disorder surrounding the Islamic Revolution, no one was known to target schoolgirls for attending classes.
Hadi Ghaemi is the executive director of the New York-based Center for Human Rights in Iran.
"There is a very fundamentalist thinking surfacing in society," Ghaemi said.
"We have no idea how widespread this group is but the fact they have been able to carry it out with such impunity is so troubling."
I'm Jill Robbins.