Alleged poisonings of Afghan schoolgirls by Taliban insurgents regularly make headlines -- but there are signs the incidents could be cases of mass hysteria, say specialists in the field.

In a widely-reported "attack" last week, more than 120 girls from a school in northern Takhar province were rushed to hospital after scores fainted and others complained of feeling ill.

Local officials accused the Taliban -- who banned schooling for girls while in power from 1996 to 2001 -- of contaminating the air with an unidentified "toxic powder".

In two other cases this year alone a "gas attack" and "poisoned water" have been blamed for mass fainting episodes in other schools.

The children are always taken to hospital and usually released shortly afterwards, with authorities vowing to submit samples taken from the girls for analysis.

Usually, nothing more is heard. But enquiries by AFP have found that neither the government nor NATO's military in Afghanistan have discovered proof of poisoning.

Instead an international expert said the cases had "all the earmarks" of mass hysteria.

"So far no evidence or any traces of any kind of poison or gas have been found" in government tests, interior ministry spokesman Sayed Edayat Hafiz said.

A spokesman for NATO's International Security Assistance Force said that at Kabul's request it had collected samples after 200 students were recently reported ill at a high school in the eastern province of Khost.

"Initial laboratory tests of multiple air, water and material samples were negative for any organic compounds like poisons or other toxic material," said Lt-Col Jimmie Cummings.

"Further tests continue, but at this point it is unlikely that any foreign substance caused the reported symptoms."

With no physical cause established, Robert Bartholomew, a sociologist and author, told AFP the poisoning scares had "all the earmarks of mass psychogenic illness, also known as mass hysteria".

Bartholomew, who is based in New Zealand, said he had collected more than 600 cases of mass hysteria in schools dating back to 1566 in Europe, "and the Afghan episode certainly fits the pattern".

"The tell-tale signs of psychogenic illness in these Afghan outbreaks include the preponderance of schoolgirls; the conspicuous absence of a toxic agent; transient, benign symptoms; rapid onset and recovery; plausible rumours; the presence of a strange odour; and anxiety generated from a wartime backdrop."

He noted there was a history of similar cases in combat zones, listing examples from the Palestinian territories in 1983 to Soviet Georgia in 1989 and Kosovo in 1990.

The Afghan incidents came "within a larger social panic involving the fear of Taliban insurgents", he added.

Afghanistan has been at war for the past 30 years, and according to the director of the government's mental health department, Bashir Ahmad Sarwari, half the population suffers from mental stress caused by the conflict.

"Two out of four Afghans suffer from trauma, depression and anxiety," he told AFP. "They are in trauma mainly because of three decades of war, poverty, family disputes and migration issues."

The Taliban on Sunday issued a statement through the Afghan Islamic Press denying responsibility for any poisoning attacks on girls' schools.

"The Islamic Emirate completely disassociates itself from such activities.

If found in any part of the country, those doing such activities would be given punishment according to Sharia," the statement said.

The Taliban's history, however, makes them an easy target for officials searching for someone to blame for the mysterious illnesses.

Before the hardline Islamists were toppled in a US-led invasion after the

9/11 attacks on New York and Washington, they were notorious for their brutal suppression of women.

Girls were not allowed an education, women were not allowed to work and those not wearing the all-enveloping burqa were whipped in the street.

NATO has some 130,000 troops in Afghanistan, but they are due to withdraw by the end of 2014, raising fears among Afghans that their country could be plunged into a new civil war -- or that the Taliban could return to power. (AP)