"The punishment for the crime of promoting and encouraging others to remove the hijab is much heavier than the crime of removing the hijab," semi-official Mehr News quoted a top official as saying.
Iran has been swept by protests since the death of 22-year-old Mahsa Amini in the custody of the country's morality police last September.
Reports now suggest schools across 21 of Iran's 30 provinces have seen suspected cases, with girls' schools the site of nearly all the incidents.
The poisoning incidents have been reported at more than 30 schools in at least four Iranian cities since November, prompting some parents to take their children out of school.
Tehran calls in Britain's charge d'affaires Isabelle Marsh, to protest allegations that Tehran made "threats" to the lives of UK-based journalists that forced the shutdown of the Iran International television operation in London.
Tens of thousands of Iranians went out to gather in public squares and streets to commemorate the 44th anniversary of the late Shia cleric Ayatollah Khomeini replacing the Shah Mohammad Reza Pahlavi.
Panahi was arrested last July when he went to the Tehran prosecutor’s office to inquire about the arrests of two other Iranian filmmakers, and was held at the Evin Prison.
Iran strongly condemned new sanctions imposed by the EU and Britain and said it would retaliate, after the West stepped up pressure on Iran over its crackdown on protests.
Iran has executed four people in connection with nearly four months of demonstrations since the death in custody of Mahsa Amini following her arrest for allegedly violating the country's dress code for women.
Three suspects were recently convicted of allegedly killing members of Iran's Basij Resistance Forces during protests in Isfahan, but rights groups question the fairness of the trials.
Iran has accused foreign adversaries of fomenting unrest, which erupted in the country three months ago after the death of Mahsa Amini, who was arrested by morality police enforcing the country's mandatory dress code laws.
Tehran is accusing hostile foreign powers and opposition groups of stoking the unrest.
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