NBC News.
Iranian authorities say they are investigating the poisoning of hundreds of schoolgirls across the country.
The mysterious incidents may have been deliberate attacks designed to prevent girls from seeking an education, officials said in recent days, after previously downplaying the issue. Girls and young women have played a prominent role in the protests that have rocked the Islamic Republic.
According to the Parliament's news agency, Khane Mellat, MP Alireza Monadi said after an investigation that nitrogen gas had appeared during testing at the schools.
Local media reports suggest the poisonings have been going on for months and involved dozens of schools in a range of cities, forcing young students to be taken to the hospital.
Iran’s police chief, Ahmad Reza Radan, said Tuesday that no one had yet been arrested.
"Our priority is to find the origin of the poisoning of the students, and until then, we will not judge whether it was intentional or unintentional,” he said in an interview with the semiofficial ISNA news agency.
Authorities have cracked down on the protests that erupted in the wake of Mahsa Amini's death.
But Deputy Health Minister Younes Panahi said Sunday the poisoning of schoolgirls in the holy city of Qom — one of Iran’s larger cities south of Tehran — and the western city of Borujerd, was not accidental and was down to people wanting to shut girls’ schools. 
“What is clear is that both in Qom and Borujerd, it is a deliberate issue,” he said at a news conference, according to Iranian state broadcaster IRIB. “The poisoning of students of Qom was intentional and caused by available chemical compounds. Some people wanted all schools to be closed, especially girls’ schools.”
Panahi added that the poisoning was due to a chemical compound which has not yet been identified, according to IRIB. “The poisoning caused to the students was very mild, and did not cause any complications to anyone,” he was reported as saying. “They had symptoms of lethargy and weakness for several hours.” 
“It has been revealed that the chemical compounds used to poison students are not war chemicals … the poisoned students do not need aggressive treatment and a large percentage of the chemical agents used are treatable.”
A special committee had been appointed to investigate the poisonings, and toxicology experts had been consulted, Panahi added.

U.N. says Iran has 'weaponized' death penalty to strike fear

Monadi, who sits on the Parliament’s education committee, also said the poisonings were “intentional,” according to the state-run news agency IRNA.
The “existence of the devil’s will to prevent girls from education is a serious danger, and it is considered a very bad news,” he said, according to IRNA.
Schools in at least 10 to 15 cities had been struggling to cope with poisoned students, MP Abdolali Rahimi Mozafari said, Khane Mellat reported. Meanwhile, Poisoning cases were reported at some 30 schools across the country, according to The Associated Press, which cited local media reports.
The first cases emerged in late November in Qom, according to the news agency, with students at the Noor Yazdanshahr Conservatory falling ill, and then falling ill again a month later. Parents in the city have pulled their children from classes in recent weeks, the AP reported, citing Shargh, a reformist news website based in Tehran.
Qom, packed with religious schools and revered shrines, is one of the country’s most important centers for Shia clerics.

Some critics of Iran’s government have have said without providing evidence that the recent spate of poisonings may be an act of “revenge” for the unrest that erupted across the country when 22-year-old Mahsa Amini died in a hospital after she was detained by the morality police, who accused her of breaking Iran’s strict dress code.
Female students in schoolyards and classrooms were at the forefront of Iran’s protests, as they stood up to strict sartorial codes by removing their headscarves and confronting officials.
“The poisoning of school girls is revenge by the terrorist Iranian regime against brave women that made the compulsory hijab the flag, and shook the Berlin wall of Khomeini,” the Iranian activist and journalist Masih Alinejad tweeted Sunday.
Another activist, Hossein Ronaghi, said on Twitter that: “In a structure where a citizen is beaten and detained by an army of privates for writing a story or graffiti against the government, it cannot be said that the deliberate and organized poisoning of Iranian girls is arbitrary and without information.”
“Attacking female students and harassing them is an attack on the future of all Iranian people,” said Ronaghi, who said he was released on bail in November after being imprisoned during the authorities’ crackdown on the protests.
Others drew different parallels but nonetheless expressed concern about the apparent trend.
Masoumeh Ebtekar, who was the country’s first female vice president after the Islamic Revolution and who has been supportive of the recent protests, said on Twitter on Monday that the poisonings had been going on for at least a month. 
“Everyone is waiting for the law enforcement and judicial departments to act immediately. Why so much delay?” she said of the Iranian authorities.