More than 100 girls were poisoned from fumes today at schools of Iranfollowing a series of similar incidents that have rocked the country since November, according to local media reports.

Students at seven girls’ schools in the city of Ardabil in northern Iran felt unwell during the morning and 108 were taken to hospital, the head of hospital services told Tasnim news agency.

The general condition of the female students, who are suffering from difficulty in breathing and nausea, is improving, the official explained.

Iranian media also reported new cases of poisoning in at least three schools in Tehran.

At a high school in Tehran, west of the capital, female students were poisoned by some kind of spray, Fars news agency reported, citing the students’ parents.

According to the estimates announced today by the representative of the Parliamentary Health Committee Zahra Sheikhi, about 800 schoolgirls have been poisoned by the respiratory tract since the end of November in the holy city of Qom and 400 in the city of Boruzerd.

According to the results of toxicological tests released by the Ministry of Health, the toxic substance used in the city of Qom consists of nitrogen-based N2 gas, which is used by industry or as an agricultural fertilizer.

Iran’s President Ibrahim Raishi today tasked Interior Minister Ahmad Vahidi to “follow up on the case as soon as possible” and “inform” the public about the results of the investigation “so as to appease the concerns of the families,” the Iranian presidency website announced .

The interior minister told reporters today that authorities are still investigating “possible persons responsible” for the poisonings, but no arrests have yet been made.

“So far, we don’t have a definitive conclusion about the composition of the toxic substance that has been used” to poison the schoolgirls, he said.

The case has sparked a wave of outrage in Iran, where the silence of the authorities in the face of the growing number of affected schools has been denounced. Some students have been hospitalized, but none have been seriously harmed.

The health ministry explained on Sunday that “certain people” they seek with their actions “to close all schools, and especially girls’ schools”.

Widely agreed, universal education is compulsory in Iran, where girls make up the majority of university students.