Local media said parents protested in Iran after dozens of schoolgirls nationwide were hospitalized in a suspected fresh wave of poisoning attacks.
Hundreds of cases of respiratory distress due to as-yet-unexplained illnesses have been reported in at least 10 of Iran's 31 provinces and more than 30 schools.
In Iran's Shi'ite Muslim holy city of Qom, a wave of sicknesses began in November, leading some parents to pull their children out of school.
According to Iranian officials, the girls may have been poisoned, who have accused Tehran's opponents.
The country's health minister has stated that the girls had been subjected to "mild poison" attacks. Some legislators have speculated that the girls may have been targeted by Islamist extremists opposed to girls' education.
On Saturday, Iran's interior minister announced that investigators had uncovered "suspicious samples" currently being analyzed.
The minister, Abdolreza Rahmani Fazli, said in a statement carried by the official news agency IRNA: "In field studies, suspicious samples have been found, which are being investigated ... to identify the causes of the student's illness, and the results will be published as soon as possible,"
Social media videos depicted parents gathering at schools to pick up their children and some pupils being transported by ambulance or bus to hospitals.
According to a video authenticated by Reuters, a protest by parents outside the Education Ministry office in western Tehran on Saturday escalated into an anti-government demonstration.
Protesters screamed, "Basij, Guards, you are our Daesh," comparing the Revolutionary Guards and other security personnel to the Islamic State.
In other films, demonstrators chanted, "They are lying that our enemy is America; our enemy is right here."
According to unverified footage, protests of a similar nature occurred in two other regions of Tehran and other cities, including Isfahan and Rasht.
Iran's clerical rulers have faced months of anti-government rallies prompted by the murder of a young Iranian lady in the hands of the morality police, who enforce stringent dress restrictions.
Recent social media posts have displayed photographs and videos of girls who have been ill, felt queasy, or experienced heart palpitations. Others reported having headaches. Reuters could not verify the posts.
On Friday, the United Nations human rights office in Geneva asked for a transparent inquiry into the alleged attacks. Other nations, notably Germany and the United States, expressed their alarm.
Schoolgirls participated in the September anti-government demonstrations. Women have removed their required headscarves in classrooms, torn up images of Supreme Leader Ayatollah Ali Khamenei, and demanded his execution.