More than 80 schoolgirls in Kunduz were taken ill
Scores of schoolgirls in the Afghan province of Kunduz have fallen ill over the past week, in what authorities allege is mass poisoning by insurgents.
On Sunday, 13 girls were taken ill. This follows two separate incidents earlier in the week when about 70 girls complained of dizziness and nausea.
An inquiry has already begun, health officials told the BBC.
The Taliban - which oppposes female education - denies carrying out an attack, the Reuters news agency says.
The girls said they noticed a strange smell in class before the onset of their symptoms, but health officials said the gas remains unidentified.
None of the symptoms experienced by the girls are reported to to be serious.
The incidents all involved different schools.
In May 2009, Afghan authorities launched an investigation after about 90 schoolgirls fell ill in Kapisa province.
Although officials suspected deliberate poisoning, the results of the inquiry were inconclusive.
In recent years there has been an increase in attacks on schoolgirls in Afghanistan, mainly in the south and east of the country where several acid attacks on schoolgirls have been reported.
Girls were banned from attending school during the rule of the Taliban, who were overthrown in the American-led invasion of 2001.