Samira, a 15-year-old student at the school, was on gate duty when she said she saw three men standing outside the school building shortly before her classmates were taken ill.

"I smelled something very sweet and when I went and told my teachers about it they said it was not a big incident," she told the Reuters news agency.

"But later on I saw girls falling down and collapsing and vomiting so we called the police."

Kabul incident

Afghanistan's interior ministry said it had no information on the Kunduz attack.

But it confirmed that six schoolgirls and one teacher from a school in Kabul were taken to a nearby clinic after smelling a gas and falling ill.

"I saw girls falling down and collapsing and vomiting so we called the police"

Samira, 15-year-old Kunduz student

"It's not clear what was the cause of the poisoning, whether it's a destructive action or a kind of gas used for something else," Zemarai Bashary, the interior ministry spokesman, said of the Kabul incident.

"But we will check whether this is an action of the enemies or food poisoning."

The suspected attacks are the latest in a series of incidents at girls' schools involving an airborne substance that officials say could be poisonous gas.

There was no immediate claim of responsibility for the incident on Tuesday, but the government has blamed the suspected attacks on fighters opposed to female education.

Taliban denial

Girls' schools have been attacked in similar fashion in other parts of Afghanistan over the past few years.

In one attack in Kandahar in 2008, around 15 girls and teachers were sprayed with acid by men on motorbikes.

During Taliban rule, from 1996-2001, girls were banned from attending school.

In parts of southern and eastern Afghanistan, particularly in Taliban strongholds, schools for girls still remain closed.

But the Taliban has denied any involvement in the recent spate of suspected attacks, and has condemned the targeting of school girls.