Iran’s supreme leader has called the suspected poisoning of Iranian schoolgirls in recent months an “unforgivable” crime amid signs that hundreds of schoolgirls have been treated in hospital, many more than the regime had previously admitted. “Authorities should seriously pursue the issue of students’ poisoning. This is an unforgivable and big crime … The perpetrators of this crime should be severely punished,” Ayatollah Ali Khamenei said. He added there would be no amnesty for those found guilty. It was his first public reaction since the suspected poisonings began three months ago. Iranian officials acknowledged the incidents only in recent weeks and have provided no details on who may be behind the attacks or what chemicals – if any – have been used. On Monday it emerged that authorities had arrested a Qom-based journalist, Ali Pourtabatabaei, who was regularly reporting on the suspected poisonings. Iranian activists and civil rights groups are calling for nationwide rallies this week to denounce the authorities’ failure to do more to investigate the poisoning No evidence has emerged that definitively links the incidents to poisoning attacks, and some experts outside Iran have said psychological factors could be playing a role in at least some of the cases. Some authorities have called for parents to show calm, with some implying mass hysteria is taking hold. Hundreds of girls in schools in at least 25 of Iran’s 31 provinces have been affected since the first report of a suspected attack in the holy city of Qom in November, according to Iranian officials. Some politicians have suggested they could have been targeted by extremist religious groups opposed to girls’ education in line with the thinking of the Taliban in Afghanistan. Jailed human rights activist Narges Mohammadi joined several teachers’ unions and student organisations calling on Iranians to take to the streets on 8 March, International Women’s Day. Panic scenes were reported in several western Kurdish towns, where dozens of schoolgirls were sent to medical centres with poisoning symptoms. “So far, the government has not prevented the continuation of this violence against our children, and has not even investigated or found any suspects,” Mohammadi said in an Instragram post. “We cannot and should not be silent about the widespread and linked poisoning of students, especially schoolgirls, during the past week. This hateful and inhumane act has not been committed only to repress protests,” she said. Mohammadi called on the UN “not to ignore this inhumane and frightening behaviour and to take immediate practical action”. Shahriar Heydari, a member of the Iranian parliament’s security commission, demanded that the country’s security council step up its inquiries into what he called an organised movement. The incidents have spread further fear among parents during months of unrest sparked by the death in custody of Mahsa Amini in September. Videos of upset parents and schoolgirls in emergency rooms with IVs in their arms have flooded social media. Some parents have taken their children out of school and held protests against the establishment. For the first time since the Islamic Revolution in 1979, schoolgirls have been joining the protests that spiralled after Amini’s death. Some activists have accused the establishment of the poisonings in revenge. On Monday there were reports of suspected poisonings affecting 39 students in Shandarman Masal, 30 students in Qochan, and 16 students and a teacher in Neishabur. A group of students from a girls’ dormitory in Mashhad were taken to hospital, as were a group of girls in Kohdasht. Habib Haibar, the vice-chancellor of Ahvaz Jundishapur University of Medical Sciences, said 1,104 schoolgirls had been treated in hospitals in Khuzestan province alone for symptoms linked to possible poisoning attacks. The rapid spread of cases has prompted some observers to draw parallels with a similar phenomenon documented by the World Health Organization in Afghanistan between 2009 and 2012, when hundreds of girls across the country complained of strange smells and poisoning. No evidence was found to support the suspicions and the WHO said it appeared to be “mass psychogenic illnesses”. UK-based experts interviewed by the BBC over the weekend did not rule out the possibility of toxic substances being involved in Iran but suggested that psychological factors could be a factor too. Unlike neighbouring Afghanistan, Iran has no history of religious extremists targeting women and girls’ education. Even at the height of the 1979 revolution women and girls continued attending schools and universities. The seriousness with which the security forces have sought out perpetrators has been contrasted with their treatment of protesters demanding the right to choose whether to wear a hijab. Theories abound in Iranian society about the cause of the incidents. Some have said the children possess a heightened sense of smell, with others blaming collective paranoia, the work of the Israeli intelligence services or reactionary zealots. The controversy has been deepened by the efforts of some conservative-minded politicians in parliament to object to any debate being held. Iran has imposed stringent restrictions on independent media since the outbreak of nationwide protests in September, making it difficult to determine the nature and scope of the incidents. Affected children have reportedly complained of headaches, heart palpitations, feeling lethargic or otherwise unable to move. Some described smelling tangerines, chlorine or cleaning agents.