Western women who join Islamic State militants are driven by the same ideological passion as many male recruits and should be seen as potentially dangerous cheerleaders, not victims, experts said Wednesday.

A new study from the London-based Institute for Strategic Dialogue (ISD) said the estimated 550 women who have travelled to Iraq and Syria are expected to marry, keep house and bear children.

But despite being banned from fighting, many are active propagandists for the cause on social media, celebrating the brutal violence of IS militants, acting as recruiting sergeants and even encouraging attacks abroad.

"The violent language and dedication to the cause is as strong as we find in some of the men," said co-author Ross Frenett, an extremism expert.

"The worry is that as ISIS (the IS group) loses ground, as everyone hopes it does, that more and more of these women will transfer from the domestic world they're in now to a more violent one," he told AFP.

Much has been written about young women going to become "jihadist brides", but the prevailing narrative of wide-eyed recruits drawn by a sense of excitement belies the importance of their own faith and passions.

The ISD researchers have been monitoring hundreds of women on social media, but focused for the study on 12 women from Austria, Britain, Canada, France and the Netherlands who are living with the IS group in Iraq and Syria.

Some of the women endorsed the bloody beheadings carried out by the militants -- "I wish I did" it, one said after US journalist Steven Sotloff was killed -- as well as railing against Western governments and the suffering of Muslims.

"My best friend is my grenade... It's an American one too. May Allah allow me to kill their Kanzeer (pig) soldiers with their own weapons," one said.

Crucially, the women also provide advice and encouragement to other women thinking of joining.

"They're actively recruiting women and providing them with assistance advice and referrals to go to ISIS-held territory," said Frenett.

"And they are acting as cheerleaders for terrorist attacks back home."

- Social media 'rebranding' -

"There has been this gender blind spot where we see women as victims rather than as potential terrorists," said Jayne Huckerby, associate professor at Duke University School of Law who specialises in women and counter-extremism.

"Policy makers have overlooked and underrated female terrorism both in terms of motivations for going and the roles that are played there."

She said many women were driven to leave Western countries because of alienation and restrictions on their freedom to practice their faith, and drawn to the IS group by a sense of adventure and enthusiasm for a new Islamic utopia.

Their key role, aside from being wives and mothers, is to paint a picture to the outside world of daily life under the militants, through postings on social media that intersperse violent videos with photos of their cooking.

"They're very important in terms of re-branding ISIS as less of a terror group and more of a state building exercise," Huckerby told AFP.

She noted that many were also willing to fight, a point also made by Melanie Smith, of the International Centre for the Study of Radicalisation (ICSR) at King's College London.

Smith, who maintains a database of about 70 female IS members, said British women are inciting attacks by suggesting them to people who could not travel to Iraq and Syria.

"You can see women online being frustrated about the fact they can't fight and they suggest to each other that they could do something else," she told The Observer newspaper.

Despite their passion, many of the women appear to find it difficult to leave their families behind, a factor which could be key to keeping them at home.

Frenett said the authorities should better support relatives, and also provide a way out for the women if they become disillusioned.

"There needs to be a path available to them when they come home," he said.