Iranian authorities announced Tuesday the first arrests linked to a series of mysterious poisonings of schoolgirls across the country.

"A number of people have been arrested in five provinces and the relevant agencies are conducting a full investigation," said Iran's deputy Interior Minister, Majid Mirahmadi, on state television.

More than 1,200 Iranian schoolgirls from at least 60 different schools have fallen ill since November from what may have been chemical or biological attacks, according to Iranian state media and government officials. That number may be far higher, with one prominent Iranian lawmaker claiming as many as 5,000 students have complained of falling ill across 230 schools, though no other officials or media have reported such a high number.

Reports of poisonings spiked over the weekend, with students describing a range of unexplained odors reminiscent of everything from paint to perfume to something burning. After the smells, they reported experiencing numbness, temporary paralysis or near blackouts. 

"It certainly sounds like a chemical or biological event," Hamish de Bretton-Gordon, a British chemical weapons expert, told CBS News. "That is not something that appears to be naturally occurring."

"Tear gas, particularly badly made tear gas, would create these sort of symptoms without killing people, and possibly other chemicals like sulphur dioxide, and some people also suggested nitrogen dioxide. These are industrial chemicals that have perfectly [legitimate] commercial uses, but can be toxic to humans in certain doses," he said. 

No deaths have been reported and nearly all of the affected girls appear to have recovered within a few days.

Iranian leaders and officials don't appear to have reached any consensus on the cause — unusual for the top-down authoritarian regime run by Islamic clerics. 

Supreme Leader Ayatollah Ali Khamenei said if the girls have been deliberately poisoned, it is "a great and unforgivable crime," punishable by death. 

State media said the Interior Ministry had found and sent suspicious samples for analysis, but the deputy interior minister had earlier suggested that "hostile" media outlets could be to blame, rather than toxins. 

"Over 99% of this is caused by stress, rumors and psychological war, started particularly by hostile TV channels, to create a troubled and stressful situation for students and their parents," Mirahmadi said previously, before announcing the arrests on Tuesday.

On the streets of the capital Tehran and other cities around the world, angry Iranian nationals have protested against the government and accused the regime of committing state terrorism against its own people. They believe Iran's leaders, or people in positions of power, could have been exacting revenge for the wave of women-led, anti-government protests that swept across the county starting last summer after the death of Mahsa Amini in police custody.

"I think you cannot underestimate the psychological impact of using chemical and biological weapons," said de Bretton-Gordon. "Certainly, any young girl in Iran thinking about protesting in future may well think twice if they think they're going to be essentially gassed because of that." 

If Iranian officials are behind the mysterious poisonings, de Bretton-Gordon said the ultimate goal would have been to silence protesters and instil fear. 

"They don't have the luxury that we do have in the democratic world to make our opinions known," he said. "In countries like Iran, any dissent is stamped on very, very quickly. That is what these autocratic governments do." 

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Ramy Inocencio

Ramy Inocencio is a foreign correspondent for CBS News based in London and previously served as Asia correspondent based in Beijing.

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