Dozens of students hospitalised in Hamedan, Zanjan, West Azerbaijan, Fars and Alborz provinces, according to local media reports.

Hundreds of cases of respiratory distress have been reported in recent months among schoolgirls around the country, mainly in the holy city of Qom, south of Tehran, with some needing hospitalisation.

The illnesses remain unexplained and Iranian officials believe the girls may have been poisoned and have blamed Tehran’s enemies.

The Tasnim and Mehr news agencies on Saturday reported the latest incidents in western Hamedan province, as well as Zanjan and West Azerbaijan in Iran’s northwest, Fars in the south and Alborz province in the north.

Dozens of students were transferred to local hospitals for treatment, the reports said.

The Reuters news agency reported that sickness affected more than 30 schools in at least 10 of Iran’s 31 provinces on Saturday.

Videos posted on social media showed parents gathered at schools to take their children home and some students being taken to hospitals by ambulance or buses.

On Friday, President Ebrahim Raisi said the suspected poisoning cases were “the enemy’s conspiracy to create fear and despair in the people”.

Iran’s interior minister on Saturday said investigators had found “suspicious samples” that were being studied.

“In field studies, suspicious samples have been found, which are being investigated … to identify the causes of the students’ illness, and the results will be published, as soon as possible,” the minister, Abdolreza Rahmani Fazli, said in a statement carried by the official news agency IRNA.

On Wednesday, at least 10 girls’ schools were targeted in suspected poisoning attacks, seven in the northwestern city of Ardabil and three in the capital Tehran, according to local media reports.

Last week, Iran’s deputy health minister, Younes Panahi, said the attacks were aimed at shutting down education for girls.

Al Jazeera’s Dorsa Jabbari, reporting from Tehran, said many parents have said that they will keep their daughters at home “until there is some answer provided by officials,” Jabbari said.

“We know that most [government schools] have security cameras outside and inside the institutions. The question now is why the officials haven’t been able to find any leads in these cases.

“This is alarming in a country where women have one of the highest literacy rates in the Middle East. Over 95 percent of women in Iran are educated and this certainly is a new phenomenon.”

The United Nations human rights office in Geneva called on Friday for a transparent investigation into the suspected attacks and countries including Germany and the United States have voiced concern.

The string of suspected poisonings came more than five months into nationwide protests following the death in custody of Iranian Kurd Mahsa Amini, 22, who had been arrested for an alleged breach of strict dress rules for women.

Tehran says hundreds of people have been killed and thousands arrested in connection with the protests, which the authorities generally describe as “riots”.