More than 100 girls have been poisoned by an unknown gas at a school in Afghanistan’s western Farah province, reportedly said Abdul Zabar Shaqaiq, the provincial public health director.

Shaqaiq indicated that “106 girls were admitted to a local hospital on Saturday afternoon and two of them are in critical condition,” Afghanistan’s TOLOnews reports.

“We could not identify the type of gas. 106 persons have been poisoned. The poisoning was not serious,” said the health director.

The incident took place in Chahar Bagh School for girls, according to Ghulam Sarwar, the acting director of education for Farah province.

Sarwar noted that investigations were underway to track down those responsible for the crime.

“A large number of students have recovered and were taken home,” he said.

“When we went to school, the gas poisoned students in a class and then it poisoned us and other girls,” Suraya, a student, told TOLOnews.

Two doctors were reportedly affected by the unknown gas after treating the students.

Khaama Press learned from provincial officials that “the students were suffering from fever and shivering when admitted to hospital.”

“The circumstances surrounding the poisoning of the school girls have not been ascertained so far,” notes Khaama Press. “This is not the first time the school girls have been poisoned during the school hours but numerous incidents have taken place in the past, specifically in northern provinces of the country.”

In September 2015, nearly 300 girls and female teachers were poisoned during three incidents at two different schools in the western Afghan province of Herat.

Members of the Taliban, which is opposed to women’s access to education, were suspected of being behind the three incidents at the private Habibul Mustafa School and the Habibul Mustafa School.

However, no specific group took responsibility for the incidents.

When it ruled Afghanistan from 1996 to 2001, the Taliban denied women and girls access to education.

The terrorist group was ousted by the U.S.-led coalition in 2001.

“Attacks against schoolgirls in Afghanistan happen with alarming frequency, often by militants who believe girls should not go to school,” reported CNN in September 2015.

“These incidents have also taken place in Kabul, Bamyan, Maidan Wardak, Jawzjan and Badakhshan provinces in recent years,” added Khaama Press.

In Afghanistan, ultra-conservative elements oppose female education.