As many as 77 primary school students, mostly girls, and their teachers are suspected to have been poisoned over the weekend and taken to hospital in Afghanistan’s Sangcharak district, Mohammad Rahmani, the head of Education Department in the northern Sar-e-Pul province, told CNN.

The intelligence unit of the provincial police department said they are still investigating the matter, according to Rahmani, who said he spoke to police directly. So far officials are unclear on the culprit, the motive, and the potential type of poison possibly used against the school children, he added.

The investigation was prompted by accounts of 17 female students in one school on Saturday, and a day later, 60 others, mostly girls, at another school in a nearby village, Rahmani said.

“After reaching school in the morning, the students suddenly started feeling dizzy, headache, and nausea,” Rahmani said. The students were admitted to a local hospital, but 14 whose condition was more critical were transported to a hospital in the provincial capital, according to Rahmani.

A doctor at Sar-i-Pul hospital confirmed to CNN that some of the girls were admitted to hospital and he believed they were poisoned based on their symptoms.

The doctor spoke on the condition of anonymity, citing safety concerns.

Education for girls is only allowed up to sixth grade in Taliban-controlled Afghanistan, so most of those poisoned were six to 12 years old.

Afghan authorities are still looking for the perpetrator. Some officials said the person behind the poisoning held a grudge but did not elaborate. Others said it results from animosity between villages, but residents and elders disagree with that claim. About half the girls were discharged from the hospital by Monday, and no fatalities were reported.