More than 100 girls were taken to hospital from their school in western Afghanistan on Monday after breathing in toxic gas, officials said, and police were investigating whether the incident was deliberate.
Elements of Afghanistan's ultra-conservative society oppose education for girls and schools have periodically come under attack.
As many as 124 girls were hospitalized in Herat province, officials said. Most were discharged the same day.
The district governor of Enjil, where the poisoning took place, blamed it on enemies of the government who opposed education for children. Police promised to track down those responsible.
During Taliban rule from 1996 to 2001, girls and women were banned from education and the workplace.
The Islamist group was ousted by a U.S.-led coalition and is now waging an increasingly violent insurgency against the foreign-backed government.