Kabul, Aug. 31: Blood tests have confirmed that a series of mysterious mass sickenings at girls’ schools across the country over the last two years were caused by a powerful poison gas, Afghan officials said today.

The sickenings had long been officially dismissed as episodes of mass hysteria, caused by the frequency of arson and acid attacks directed at schoolgirls by the Taliban and other extremists who oppose their education.

How the gas was delivered remained a mystery, the officials emphasised. There have been no fatalities, and no one has ever claimed responsibility for the episodes. But the cases have been reported only in girls’ schools, or in mixed schools during hours set aside only for girls. Blood samples from victims in 10 attacks over the past two years showed toxic levels of organophosphates, according to Dr Kargar Norughli, spokesman for the ministry of public health, who said his ministry and the WHO carried out the tests at laboratories in Turkey.

Organophosphates are widely used in insecticides and herbicides, and are also the active ingredients of compounds developed in the past as chemical weapons, including sarin and VX gas. Blood samples taken in the past week from more than 100 girls as well as a few teachers, from two girls’ schools in Kabul are still being analysed, Dr Norughli said, but their symptoms were similar to those in the 10 cases where the poisonings were confirmed. A spokeswoman for WHO in Afghanistan, Aanchal Khurana, said that she could not immediately confirm the results of the earlier tests.