TALUQAN   - As many as 74 schoolgirls in Afghanistan's far north fell sick after smelling gas and were being examined for possible poisoning, local officials said on Sunday.

While instances of poisoning are sometimes later found to be false alarms, there have been numerous substantiated cases of mass poisonings of schoolgirls by elements of Afghanistan's ultra-conservative society that are opposed to female education.

Local officials said the girls became ill after smelling gas at their school, Bibi Maryam, in Takhar province's capital, Taluqan. The city is about 250 kilometres north of the country's capital, Kabul.

The Takhar governor's spokesman, Sulaiman Moradi, blamed "enemies of the government and the country" for the mass illness and said the aim was to stop girls from going to school.

The girls were taken to the provincial hospital and most were released after being treated, though several remained in a critical condition on Sunday evening, the head of the hospital, Dr Jamil Frotan, said.

"We have already sent samples of their blood to the Ministry of Public Health and it will soon become clear what the reason for their illness was," Frotan said.

The apparent poisoning came three days after more than a dozen students fell ill in another girls' high school in Taluqan. No-one has claimed responsibility for either incident. Between May and June last year there were four poisoning attacks on a girls' school in Takhar, prompting local officials to order principals to stay in school until late and staff to search the grounds for suspicious objects and to test the water for contaminants.

Takhar has been a hotbed of militancy and criminal activity since 2009, with groups such as the Taliban and the Islamic Movement of Uzbekistan active.

Since the 2001 ousting of the Taliban, which banned education for women and girls, females have returned to schools, especially in Kabul. But periodic attacks against female students, their teachers and their school buildings, continue.

Afghan women have won back basic rights in education, voting and employment since 2001, but fears are growing that such gains could be traded away as Western forces prepare to leave and the Afghan government seeks peace talks with the Taliban.

AFP adds: Six Afghan police were killed Sunday in a Taliban raid helped by an ‘insider’, officials said, the latest attack involving Western-trained security forces turning on their own allies.

Militants stormed a police post in Deh Yak district of central Ghazni province and killed the six officers as they slept, an official said. "One of the police who had links with the Taliban let them into the post while other police were sleeping. The Taliban were led to the post and killed six police," district chief, Fazul Ahmad Tolwak told AFP.

"The police who led the Taliban into the post joined the Taliban after the attack and went with them."

He said one officer was wounded but survived the attack. Another police officer was detained over suspected links to the attack and was being investigated, he said.

Fazul Sabawoon, a spokesman for the Ghazni provincial administration also confirmed the incident and said six officers, part of the Afghan Local Police, a US-funded community force, were killed in the pre-dawn raid.

He also blamed an "insider" for the attack.

More than 60 foreign soldiers were killed in 2012 in insider attacks that have bred mistrust and threatened to derail the process of training Afghan forces to take over security duties ahead of NATO's withdrawal next year.

Scores of Afghan forces have also died in the attacks and the threat has become so serious that foreign soldiers working with Afghan forces are regularly watched over by so-called "guardian angel" troops to provide protection.