Radicalised young women who join Islamic fundamentalists fighting in Iraq and Syria pose a terror threat to the UK when they eventually return home, according to experts.

Researchers who have looked into why Western women are joining Islamic State (IS) revealed some were now willing to go against the terror group's strict rules banning them from acts of violence.

The study into the disappearance of six British women, including Scots-born Aqsa Mahmood, 20, from Glasgow, found many Western women in IS were "desensitised" to the beheadings of hostages such as Perth-raised aid worker David Haines.

Studying social media accounts, the London-based Institute for Strategic Dialogue found one of the radicalised women described the murder of US aid worker Peter Kassig and 18 Syrian hostages as "gut-wrenchingly awesome".

Ms Mahmood, a former pupil at the private Glasgow girls school Craigholme, reportedly married a militant last year, although she has since suggested in a blog that he has been killed.

Her parents, Khalida and Muzaffar Mahmood, have launched an impassioned plea calling for her to return despite what they view as a betrayal of their values.

They described her as a 'sweet, peaceful, intelligent' young woman who had previously lived a typical western lifestyle. Similar appeals have been made from the families Samya Dirie, 17, from London, and Bristol schoolgirl Yusra Hussien, 15, following fears they had travelled to Syria.

The researchers believe these appeals have an impact and could yet persuade them them to return to the UK.

Umm Ubaydah, a female European jihadist, questioned on social media whether she could "pull a Mulan and enter the battlefield", while another British woman, Umm Khattab, described how she put on an explosive belt after hearing gun shots, according to the report.

The report's authors said: "It is possible to suggest that, as the conflict drags on, the death of male fighters and the deaths of the migrant children could be a potential trigger which propels the women into changing roles.

"They may wish to strike at the 'near enemy' or even return home to strike at the West. The women's social media postings indicate that a sudden shift in roles is possible."

Around 3,000, including as many as 550 women, are thought to have travelled to Iraq and Syria, the researchers found.

The report gathered evidence from social media accounts including Twitter and Tumblr, photographs, online interactions and media reports.

Ubaydah's mention of "Mulan" - the ancient Chinese figure who impersonates a man to replace her father in the army - is a "clear reference to a Disney film" and a reminder that the women have "grown up around Western films and music", the report said.

It said the women "celebrate the violence of Isis unequivocally".

One British woman, Umm Hussain - named in reports as mother-of-two Sally Jones from Kent - tweeted: "Know that we have armies in Iraq and an army in Sham of angry lions whose drink is blood and play is carnage."

Another woman, who tweeted about the murder of Mr Kassig, said: "So I finally watched (latest IS video)...Gut-wrenchingly awesome."

One woman tweeted: "So many beheadings at the same time, Allahu Akbar (God is the greatest), this video is beautiful."

There is also evidence to suggest that women's families have a "strong influence" in persuading them not to join IS, the report said.

Umm Layth, the name Ms Mahmood goes under on social media wrote: "When you hear them sob and beg like crazy on the phone for you to come back it's so hard."

Yusra, 15, left her home in Easton, Bristol, and is thought to have met up with a 17-year-old Samya from London and boarded a plane to Turkey before the pair tried to cross the border with the war-torn state.

It is unclear how the teenagers, who are both from Somali families, met but they both vanished from their homes amid concerns they had been radicalised.

The report concludes that the threat posed by women in IS "is a different one than that posed by their male counterparts".

"They support male fighters in a non-military capacity and encourage attacks on the West by those who cannot travel," the authors said. "They demonstrate support for brutal violence equal in its strength to the men of Isis.

"They also demonstrate a capacity and willingness to engage in violence and even suicide attacks should circumstances change."