Farzana, an eight-year-old Afghan school girl looks on as she recovers in a hospital after falling ill at a school in Kapisa province on Tuesday. (Rafiq Maqbool/Associated Press)

For the third time in less than three weeks, Afghan officials are investigating whether scores of schoolgirls who had to be hospitalized Tuesday were poisoned.

Five of the girls briefly slipped into comas after falling ill Tuesday morning at a school in that Kapisa province north of Kabul, the province's chief of public health, Wahid Rahim, told Reuters.

At least 98 people were admitted to hospital after complaining of symptoms like headaches, vomiting and shivering, said Aziz Agha, a local doctor. That number includes 84 students, 11 teachers, two cleaners and the principal.

The students were lining up outside their school in northeastern Afghanistan on Tuesday morning when a strange odour filled the yard, and one girl collapsed, said the principal, Mossena, who was herself in a hospital bed gasping for breath as she described the event.

"We took her inside and splashed water on her face," said Mossena, who like many Afghans goes by one name. Then other girls started passing out, and all the students were sent home.

Mossena said she did not know what happened next because she collapsed and woke up in the main hospital in Muhmud Raqi, the capital of Kapisa province, just northeast of Kabul. It is still unclear if the illnesses were result of a direct attack on the girls, and no one has claimed responsibility.

Interior Ministry spokesman Zemeri Bashary said officials suspect some a form of gas poisoning, and that police were still investigating. Blood samples from the schoolgirls had been sent to medical authorities in Kabul for testing, said hospital officials.

But the chief of security in the area, Sha Agha, told Reuters that "people who collaborate with and support the Taliban have done this." He qualified his comments by saying he did not believe the Taliban were responsible for the illnesses.

The Taliban has opposed female education in the past. The hardline group banned girls from attending schools when it ruled Afghanistan from 1996 to 2001.

Psychological factors a possibility

Tuesday's incident comes a day after schoolgirls took ill under similar circumstances. One teacher and 61 students in nearby Charikar were taken to hospital after they reported encountering a strong, sweet smell during classes.

Similarly, schoolgirls in the same town, which is the capital of the province of Parwan, became ill in April after inhaling what witnesses described as strong fumes.

Authorities suspect the girls were the victims of a poison gas attack, but local doctors have not been able to identify the offending substance.

Blood samples taken from the affected girls for testing have not yet been analyzed. Nizamuddin Rahimi, a provincial education official, tried to downplay the incident, suggesting it was a panic attack after the students saw one of their colleagues collapse.

Research has borne out the possibility that the perception of illness could be triggered solely by psychological factors.

At a Tennessee school in 1998, 38 people were hospitalized with complaints of dizziness, headaches, nausea and shortness of breath after a teacher noticed a gasoline smell in a classroom, according to a study in the New England Journal of Medicine. The study found there had been no toxic exposure and the sickness appeared to be psychological.

With files from The Associated Press