Britain's Observer newspaper yesterday quoted a diplomatic official connected to the investigation as saying: 'This phenomenon has not been really taken into account yet and we need to explore and understand it. It is a new strategy by Al-Qaeda.'

Security officials are concerned about the increasing radicalisation of women, whose involvement in militant activity, they say, ranges from logistics and propaganda to suicide bombing.

Now, European counterterrorism coordinator Gilles de Kerchove has reportedly asked British, French, Spanish, German and other European security services to pool their intelligence via Brussels' strategic analysis unit, the Joint Situation Centre. It is expected to produce a report on the threat later this year.

Meanwhile, security officials have highlighted Britain as being particularly at risk, and say they are especially worried about women bombers being sent to Europe from North Africa.

Speaking about the overall phenomenon of female militancy, a French intelligence specialist told the Observer: 'This is now of a much greater scale than we have ever seen.'

An EU official confirmed the level of concern, saying: 'The issue is a very high priority.'

Security officials were quoted as saying that, so far, there has been only one known European female suicide bomber: 38-year-old Belgian convert Muriel Degauque, who killed herself in Iraq in 2005.

Women's involvement in militant activity in Britain has also been limited so far.

But the French intelligence specialist warned: 'Time and again we have seen Al-Qaeda trying tactics in one place and, if they work, trying them again elsewhere.'

The use of female suicide bombers has reportedly become commonplace in Iraq and Algeria, as it is easier for women to get past increasingly tight security measures.

As well as attracting less suspicion than men, it is easier for them to disguise explosives under their clothes. Male soldiers are also unwilling to search them.

The issue remains controversial within militant circles, however, with Al-Qaeda leader Ayman Al-Zawahiri provoking fierce debate recently when he said that women should restrict themselves to looking after the homes and children of fighters.