The incident took place in Ahan Dara Girls' High School in Taloqan city, the capital of Takhar province, an official with the education department told dpa.

"The students were taken to the provincial hospital and some other medical facilities," Jan Mohammad Nabizada said, blaming Taliban insurgents for attack.

Taliban last week denied involvement in attacks on schools, and demanded the punishment of those responsible.

Girls were not allowed to attend school during the Taliban's 1996-2001 rule.

Earlier, the country's intelligence agency said Taliban had increased attacks on schools and students to intimidate families into not sending their children to school.

Takhar health official Hafizullah Safi told dpa that the incident was under investigation, but said it was not known "if anyone had in fact released poisonous gas."

"Even if few students might have taken in poisonous gas, others might have lost consciousness due to fear and hysteria," the official said.

He said that a problem with drinking water in a school in Rustaq district last month that hospitalized hundreds of students was "not due to poisoning of the water but due to bacteria found in the water."