The incident took place in a Bibi Hajera Girls' High School in the provincial city capital of Taloqan, Jan Mohammad Nabizada, an education official, told dpa.

The victims were taken to hospital, he said, blaming the Taliban for the attack.

However, the Taliban, in a statement on Sunday, rejected any involvement in "anti-education activities", saying foreign forces and the Kabul administration were behind the "psychological war to defame" the Taliban movement.

"We never oppose education... We want the criminals who burn schools and poison students to be punished based on Islamic judicial rule," Taliban spokesman Zabiullah Mujahid said in a statement.

Sunday's attack was the second such incident in the same girls' school within a week, and third in the province within a month. On Thursday 130 girls and three teachers fell ill when a similar mysterious poisonous gas was released in the school.

Last week, the Afghan intelligence agency accused the Taliban of increasing their attacks in the country, especially girl's schools.

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

Afghan Education Minister Farooq Wardak earlier this month said at least 550 schools remain closed due to insecurity, affecting more than 300 000 students in 11 provinces where the insurgency is still strong.