Families have protested in Tehran after several hundred cases of gas poisoning of girls in more than 52 schools in the last three months.
The “chemical compounds” caused them to vomit, and become dizzy.
More than a thousand students have fallen ill and an unknown number were admitted to hospitals.
In his first comments on the mystery poisonings, Iran’s Supreme leader Ayatollah Ali Khamenei said those behind the poisoning should face “severe punishment”.
He also said it’s “a serious and unforgivable crime and there will be no amnesty for the perpetrators”.
Late Sunday, Iranian President Ebrahim Raisi denounced the poisoning cases as “a new conspiracy by the enemies” of Iran.
This action, Raisi said, was meant to “instill fear in the hearts of students, children and their parents”.
The Judiciary Chief Gholamhossein Mohseni Ejei said on Monday anyone arrested would be put on trial and charged with “corruption on earth” which would lead to the death penalty.
There were more than 700 similar cases reported in the southwestern province of Khuzestan on Sunday.
The authorities have not yet identified the gas used or the reasons why the girls were attacked in this way.
Last week, deputy health minister Younes Panahi said that the suspected attacks were aimed at shutting down education for girls.
The poisonings began last November, against the backdrop of anti-government protests that erupted across the country in September after the death of a young woman, Iranian Kurd Mahsa Amini, who was 22 years-old, following her arrest for allegedly breaching Iran’s strict dress code for women.