(CNN) — Concern is growing in Iran after reports emerged that hundreds of schoolgirls had been poisoned across the country in recent months.

On Wednesday, Iran's semi-official Mehr News reported that Shahriar Heydari, a member of Parliament, cited an unnamed "reliable source" in saying that "nearly 900 students" from across the country had been poisoned so far.

The first reported poisonings happened in the city of Qom on November 30, when 18 schoolgirls from one high school were hospitalized, according to Iranian state media. In another incident in Qom on February 14, more than 100 students from 13 schools were taken to hospitals after what the state-affiliated Tasnim news agency described as "serial poisonings."

There have also been reports of schoolgirls being poisoned in the capital Tehran — where 35 were hospitalized on Tuesday, according to Fars News. They were in "good" condition, and many of them were later released, Fars reported. State media have also reported student poisonings in recent months in the city of Borujerd and in Chaharmahal and Bakhtiari Province.

Many of the reports involve students at girls' schools, but state media have also reported at least one incident of poisoning at a boys' school, on February 4 in Qom.

CNN has reached out to one of the schools named by state media as having had an incident of poisoning, Noor Yazdanshahr Conservatory in Qom, as well as to individual teachers, but has not heard back.

Iranian Health Minister Bahram Einollahi, who visited affected students in Qom, said on February 15 that the symptoms included muscle weakness, nausea, and tiredness, but that the "poisoning" was mild, according to a report in state media outlet Iranian Students News Agency.

Einollahi said his team had taken many samples from patients admitted to one Qom hospital for further testing at Iran's renowned Pasteur Institute, which reported that no microbes or viruses had been identified in the samples, according to ISNA.

It's unclear if the incidents are linked and if the students were targeted. But Iran's Deputy Health Minister in charge of Research and Technology Younes Panahi said on February 26 that the poisonings were "chemical" in nature, but not compound chemicals used in warfare and the symptoms were not contagious, according to IRNA.

Panahi added that it appears that the poisonings were deliberate attempts at targeting and shutting down girls' schools, according to IRNA.

"After the poisoning of several students in Qom ... it became clear that people wanted all schools, especially girls' schools, to be closed," Younes Panahi told a news conference Sunday, according to Iranian state media outlet IRNA. He later retracted the comment, saying he was misquoted, Fars news said.

But a mother of two girls in Qom told CNN that both of her daughters had been poisoned, at two different schools, and one of them had experienced significant health issues after being poisoned last week. She spoke on the condition of anonymity due to the sensitivity of the reports, and fears for her family's safety.

"One of my daughters was poisoned in school last week," the mother told CNN on Tuesday. She said they spent two days at Shahid Beheshti Hospital in Qom along with several other schoolchildren and staff. Her daughter experienced nausea, shortness of breath and numbness in her left leg and right hand, she said.

"Now she has trouble with her right foot and has difficulty walking," the mother said.

Rising calls

Local activists and national political figures have called for the government to do more in investigating the poisonings.

"The poisoning of students at girls' schools, which have been confirmed as deliberate acts, was neither arbitrary nor accidental," tweeted Mohammad Habibi, spokesman for the Iranian Teachers Trade Association on February 26.

Habibi is among a growing number of people who believe that the poisonings may be linked to the recent protests under the "Women, Life, Freedom" movement. The movement has been characterized by women's and young girls' outpouring of anger over issues ranging from freedoms in the Islamic Republic to the crippling state of the economy.

"To erase the gains on freedom of clothing, [the authorities] need to increase public fear," he tweeted.

United States Department of State Spokesperson Ned Price called the reports of poisoning schoolgirls "very disturbing," during a briefing Wednesday.

"We've seen these reports, these are very disturbing, these are very concerning reports," Price said. "To poison girls who are simply trying to learn is simply an abhorrent act."

Price urged "Iranian authorities to thoroughly investigate these reported poisonings and do everything they can to stop them and to hold accountable the perpetrators."

In mid-February Tasnim reported that Iran's Minister of Education, Yousef Noori, said "most" of the students' conditions were caused by "rumors that have scared people," and that "there is no problem." He said that some students had been hospitalized due to "underlying conditions," according to Tasnim.

Dan Kaszeta, a London based defense specialist and an associate fellow at the Royal United Services Institute, spoke to CNN about the difficulties authorities may face in confirming reports like these.

"Unfortunately, it can be very difficult to investigate such incidents. Often, the only way to discover the causative agent is to collect samples at the time of dissemination, and this is usually difficult or impossible," he said.

"These current incidents in Iran are remarkably similar to dozens of incidents at schools in Afghanistan since approximately 2009. In a few of these incidents, pesticides were strongly suspected, but most of the illnesses remain unexplained," he added.

Kaszeta went on to explain that smells are difficult to use as an indicator. "Some things have smell added to them as the underlying dangerous chemical may be odorless."

Jamileh Kadivar, a prominent Iranian politician and former member of parliament, also believes that there is malicious intent behind the poisonings. "The continuity and frequency of poisonings in schools during the past three months proves that these incidents cannot be accidental and are most likely the result of organized group actions directed by think tanks and aimed at specific goals," she wrote in an Op-Ed in Iran's state-run newspaper Etelaat.

Iranian Education Minister Yousef Nouri visited some of the students who were hospitalized in Qom after the string of school poisonings in mid-February, and said that a special team had been formed in Tehran to follow up on the issue, according to a report in Tasnim, a state-affiliated media outlet.

Iran's national police chief, Ahmadreza Radan, said on February 28 they are investigating the cause behind the "poisonings" and that no one has been arrested with the authorities still trying to determine whether the alleged poisonings are intentional or not, according to IRNA.

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