"I think some radical elements who oppose girls going to school are behind this act," said district governor Mohammad Hussain, adding that police were looking into the incident.

The schoolgirls fell ill after drinking water from a tank at their high school in the small town of Rustaq in the northeastern province of Takhar, Hussain said.

Education ministry spokesman Abdul Saboor, however, cautioned against jumping to conclusions about the cause of the incident.

"According to our reports a number of these schoolgirls were panicked and taken to hospital and they were then quickly dismissed.

"But some others are still there. We think it is a small incident, but we are continuing our investigations."

Afghan girls were banned from going to school or working in offices by the hardline Islamist Taliban regime until it was overthrown by a US-led invasion in late 2001 for sheltering Al-Qaeda leader Osama bin Laden.

The Taliban have since waged an insurgency against the Western-backed government of President Hamid Karzai and some 130,000 NATO troops in the country.

Millions of girls now go to school, but they and their teachers are occasionally attacked.

Provincial health director Hafizullah Safi said 140 schoolgirls had been admitted to local health facilities but most were released after recovering from symptoms which included headache and nausea.

"Most of the schoolgirls who were brought to the hospital after falling ill have been dismissed, the other girls in the hospital are in stable condition,"

he said.

In similar cases last year hundreds of girl students were taken to hospitals across the country after falling ill from suspected gas attacks or water poisoning.

Authorities at the time mostly blamed the Taliban, though some suggested that the cause might have been mass hysteria, a phenomenon recorded around the world, often among young girls. (AFP)