It's believed the action is deliberate
At least 650 schoolgirls in Iran have been poisoned by toxic gas since November.
It's believed that the release of fumes into classrooms is a deliberate attempt to force their schools to shut.
Nobody has died, but students have suffered headaches, respiratory problems, dizziness and nausea.
Protests have been rife in Iran since the death of a 22-year-old woman last September, for an alleged violation of its strict dress code for women.
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