More than 5,000 cases of poisoned school pupils have been reported across the country, an Iranian MP said, as attacks spread to public transport networks.
The poisonings were a result of "special gas", MP Mohammed Hassan Asefari told the Iranian Students' News Agency.
The number those affected was significantly higher than official estimates of about 1,000.
The Czech Republic-based Radio Farda reported around 2,500 cases in more than 100 schools, according to Iranian media outlets.
First reported in the holy city of Qom in November, the poisonings have increased in recent weeks and prompted renewed anti-government protests and pushed parents to take their children out of school.
While authorities have placed the blame with Tehran's enemies, many accuse the government, pressured by months of fierce protests, of being behind the attacks.
Parents gathered outside the Ministry of Education at the weekend, in video footage verified by Reuters.
"Basij, Guards, you are our Daesh," they chanted, likening security forces to ISIS.
The Islamic Revolutionary Guard Corps and its Basij paramilitary force have been at the forefront of the regime's response to the protests and are estimated to have killed more than 500 people since demonstrations began in September.
Pro-protest accounts also reported renewed rallies in several areas, with people demonstrating against the "baby-killing government".
Schoolgirls are said to be the most affected but cases have also been reported at universities and at boys' schools.
The health ministry has claimed that "no toxic traces" were found in medical samples taken from students at affected schools.
Supreme Leader Ayatollah Khamenei said those responsible should be executed.
The poisonings have been widely condemned and the US has said it may fall under the mandate of a UN investigation.
While the government has pledged a full investigation, it has opened legal cases into news outlets for "spreading lies" about the attacks which have left some students in critical condition.
The judiciary has opened lawsuits against six news outlets and media personalities for "publishing lies and baseless rumours", its affiliated news agency Mizan reported.
Special branches have been set up across the country to deal with false rumours, it announced on Monday, and two additional branches have been established within Tehran's Special Prosecutors Office.
Meanwhile, people have also reported poisonings at metro stations in several cities, prompting fears the attacks could target wider society.
Footage on social media show travellers coughing and collapsed on metro platforms, while others have published images of emergency hammers removed from carriages, claiming they fear it is a prelude to similar attacks.
Civil rights advocate Atena Daemi also alluded to possible attacks on the metro.
"The Islamic Republic collected emergency hammers and replaced the subway windows, which is a warning for more extensive chemical attacks by government agents," said Ms Daemi, who has been imprisoned in Tehran's notorious Evin prison and has a wide following on social media.
On Tuesday, social media users warned people away from a metro station in the city of Isfahan, claiming passengers had begun collapsing and vomiting, while people reportedly fainted at a Tehran station.