LONDON (REUTERS) - Western women joining the Islamic State in Iraq and Syria (ISIS) militant group are increasingly from comfortable backgrounds and often well educated with romantic notions of adventure which are usually quickly dispelled by the harshness of life as a "Jihadi bride", according to a British research report.

Some 550 women from Western countries have left their homelands to join ISIS, which has captured swathes of Syria and Iraq, said the report by the Institute for Strategic Dialogue and the International Centre for the Study of Radicalisation at King's College, London.

However, very little was being done to explain why there had been this "unprecedented surge" to ISIS, also known as IS or ISIL, or to take preventative action.

"Western female recruits to ISIS are breaking previous stereotypes about who is 'at risk' of radicalisation into jihadism and violent extremist networks," said the report titled "Till Martyrdom Do Us Part".

It said female recruits were increasingly younger, some from comfortable backgrounds and often well-educated, and were playing "crucial" propaganda and recruitment roles.

Based on the social media activity of more than 100 Western women who are thought to have joined the militants, researchers said there were many differing reasons why women join.

"The assumption that females join ISIS primarily to become'jihadi brides' is reductionist and above all, incorrect," said the report.

Like Western men who have joined ISIS, the women felt socially and culturally isolated, believed Muslims were being persecuted and were angry that nothing was being done about it.

They were also attracted by an idealistic view of religious duty, a sense of sisterhood, and the romance of the adventure. However, life under ISIS was far from the image they saw portrayed online. Conditions were harsh and some became widows at a young age.

"The responsibility of Western women under ISIS-controlled territory is first and foremost to be a good wife to the jihadist husband they are betrothed to and to become a mother to the next generation of jihadism," the report said.

"However, there are also insights into the complaints of daily life for females, often domestically isolated in severe conditions, and the realities of living within a war zone in a terrorist-led territory."

The report concluded there was a need for'counter-extremist' messages to be aimed specifically at women, detailing how life under ISIS is far removed from the idealised view, and better programmes for those returning from Syria and Iraq to counter radical ideology and reintegrate.