At least 650 girls have been poisoned by toxic gas in Iran since November, in what many believe is a deliberate attempt to force their schools to shut.
No girls have died, but dozens have suffered respiratory problems, nausea, dizziness and fatigue.
“It became evident that some people wanted all schools, especially girls’ schools, to be closed down,” the deputy health minister said on Sunday.
However, he later said that his remarks had been misunderstood.
The prosecutor general announced last week that he was opening a criminal investigation, but he said that the available information only indicated “the possibility of criminal and premeditated acts”.
Meanwhile, public frustration is continuing to grow.
The first poisoning took place on 30 November, when 18 students from the Nour Technical School in the religious city of Qom were taken to hospital.
Since then, more than 10 girls’ schools have been targeted in the surrounding province.
At least 194 girls are reported to have been poisoned in the past week at four schools in the city of Borujerd, in the western province of Lorestan.
The poisoned girls have reported the smell of tangerine or rotten fish before falling ill.
Earlier this month, at least 100 people protested outside the governor’s office in Qom.
“You are obliged to ensure my children’s safety! I have two daughters,” one father shouted in a video widely shared on social media. “Two daughters… and all I can do is not let them go to school.”
“This is a war!” declared a woman. “They are doing this in a girls’ high school in Qom to force us to sit at home. They want girls to stay at home.”
Some parents have said their children were ill for weeks after the poisoning.
Another video from a hospital shows a teenage girl lying dazed on a bed, with her mother beside her.
“Dear mothers, I’m a mother and my child is in a hospital bed and her limbs are weak,” says the distraught mother. “I pinch her but she doesn’t feel anything. Please don’t send your children to school.”