Iran's ruler Ali Khamenei said Monday that poisoning of schoolgirls in recent months is an "unforgivable" crime and denied any government role in the attacks.

"Authorities should seriously pursue the issue of students' poisoning. This is an unforgivable crime... the perpetrators of this crime should be severely punished," Ayatollah Ali Khamenei was quoted as saying by state media.

The first incidents of chemical attacks on girls’ schools began in November, but officials first ignored the incidents until they began to spread to several cities in February. Khamenei had so far remained silent while other officials were blaming foreign enemies and regime opponents without showing any proof.

Over a thousand Iranian girls in different schools have suffered "mild poison" attacks since November, according to state media and officials, with some politicians suggesting they could have been targeted by religious groups opposed to girls' education.

However, citizens and critics on social media ask why the government has failed to arrest the perpetrators of such a large and coordinated campaign, while it was efficient in killing and detaining antigovernment protesters.

Other say the hardliner establishment is behind the attacks to take revenge from schoolgirls who joined the Woman, Life, Freedom protests in October and November.

The spreading attacks that started in the holy Shi'ite Muslim city of Qom in central Iran have spread to at least 25 of Iran's 31 provinces, prompting some parents to take their children out of school and hold protests against the establishment.