They say it is still not clear what caused the suspected poisoning, at least the third within a week.

The girls have been treated in hospital and are reported to be in good health.

Over the weekend the Taliban denied carrying out such attacks, but correspondents say local Taliban groups acting independently have admitted responsibility for some of them.

Correspondents say that because the insurgent group is not thought to have any centralised leadership, regional Taliban groups often operate with some autonomy.

The Taliban in Paktia province were recently reported to have made threats against some schools.

Some officials have attributed the attacks – in which the air is allegedly contaminated with an unidentified toxic powder or liquid – to mass hysteria among schoolgirls.

They point out that tests carried out by Nato show that few if any pupils who complained of nausea and dizziness have displayed long term symptoms of poisoning.

But others say that the scale and frequency of the attacks cannot all be because of hysteria.

The Taliban banned schooling for girls while in power from 1996 to 2001.

The Afghan education ministry recently blamed the Taliban for the closures of more than 500 schools in 11 provinces where they had strong support.

However a Taliban spokesman over the weekend told the BBC that they condemned any attacks on schools and would punish anyone who carried them out “in line with Sharia [law]”.