Hundreds of girls and women are going missing in the West, reappearing in Iraq and Syria to marry Islamic State extremists.

Girls as young as 14 or 15 are travelling mainly to Syria to marry militants, bear their children and join communities of fighters, with a small number taking up arms. Many are recruited via social media. Women and girls appear to account for about 10% of those leaving Europe, North America and Australia to link up with militant groups including Islamic State, Isis.

France has the highest number of female recruits with 63 in the region – about 25 of the total – and at least another 60 believed to be considering the move.

In most cases, they appear to have left home to marry extremists drawn to the idea of “supporting brother fighters” and “having children to continue the spread of Islam”, said Louis Caprioli, former head of the French security agency Direction de la Surveillance du Territoire. If their husband dies, they will be given adulation as the wife of a martyr.

Five people, including a sister and brother, were arrested in France this month on suspicion of belonging to a ring in central France that specialised in recruiting young French women, according to Bernard Cazeneuve, the interior minister.

Counter-terrorism experts in Britain believe about 50 British girls and women have joined Isis, about a 10th of those known to have travelled to Syria to fight.

Many are believed to be based in Raqqa, the eastern Syrian city that has become an Isis stronghold.

Twin sisters Zahra and Salma Halane, 16, left their home in Chorlton, Manchester, in July without their parents’ knowledge to follow their brother to Syria.

The girls – whose parents came to Britain as refugees from Somalia – passed their GCSEs last summer and went on to study at sixth form college. They left home in the middle of the night and were reported missing by their parents.

Now, both are reportedly married to Isis fighters. A social media account believed to belong to Zahra shows her in a full veil posing with an AK-47 and kneeling in front of the Isis flag.

Those identified by researchers at the International Centre for the Study of Radicalisation at Kings College London are mainly aged between 16 and 24.

Many are university graduates and have left behind caring families.

Another woman from Britain, Aqsa Mahmood wrote in a blogpost earlier this month, “Most sisters I have come across have been in university studying courses with many promising paths with big happy families and friends and everything in the Dunyah material world to persuade one to stay behind and enjoy the luxury.

“If we had stayed behind, we could have been blessed with it all – from a relaxing and comfortable life, to lots of money. Wallahi I swear that’s not what we want.”

At least 40 women have left Germany to join Isis in Syria and Iraq in what appears to be a growing trend of teenagers in that country becoming radicalised and travelling to the Middle East without their parents’ permission.

“The youngest was 13,” Hans-Georg Maassen, president of the Federal Office for the Protection of the Constitution told the Rheinische Post. Four underaged women left with a romantic idea of marriage and married young male militants who they got to know via the Internet.

In Austria, the case of two teenage friends Samra Kesinovic,16 and Sabina Selimovic,15, who ran away from their homes in Vienna to join militants in Syria may be only the “tip of the iceberg”, said Heinz Gartner, director of the Austrian Institute for International Politics. An estimated 14 women and girls are known to have left Austria to fight in the Middle East, according to the interior ministry.

The United States does not have data available on women and girls joining Isis fighters in Syria, a senior intelligence official said in an e-mailed statement.

“We do not have numbers to share on the number of women linked to Isis or fighting for them,” the official said.

Daveed Gartenstein-Ross, a counter-terrorism expert at the Washington-based Foundation for Defence of Democracies, downplayed the issue in the US, saying the number of women and girls joining Isis was of concern, but not an epidemic. “It’s a threat but it’s (one) among many potential threats coming out of Syria,” he said.

Karim Pakzad, of the French Institute of International and Strategic Relations, said some young women “had an almost romantic idea of war and warriors. There’s a certain fascination even with the head and throat-cutting. It’s an adventure”.

Some may feel more respected and important than in their home countries, he added.

But Shaista Gohir, of the UK Muslim Women’s Network, said little was known about the young women’s motivation or what happened to them after leaving home.

“Some of these girls are very young and naive, they don’t understand the conflict or their faith and they are easily manipulated. Some of them are taking young children with them; some may believe they are taking part in a humanitarian mission,” she said.

Social media plays a crucial role in recruiting young women to join Isis in the Middle East, according to many experts.

Some British women and girls have posted pictures of themselves carrying AK-47s, grenades and in one case, a severed head, as they pledge allegiance to Isis. But they also tweet pictures of food, restaurants and sunsets to present a positive picture of the life awaiting young women.

Mia Bloom, a security studies professor at Massachusetts University and author of Bombshell Women And Terrorism, said the recruitment campaign painted a “Disney-like” picture of life in the caliphate. Some young women were offered financial incentives such as travel expenses or compensation for bearing children.

Women living amid Isis fighters used social media adeptly to portray Syria as a utopia and to attract foreign women to join their “sisterhood in the caliphate”, she said.

“The idea of living in the caliphate is a very positive and powerful one that these women hold dear.”

But the reality was very different, she said.

Bloom and Rolf Tophoven, of Germany’s Institute for Terrorism Research and Security Policy, said reports indicated that women had been raped, abused, sold into slavery or forced to marry.

“Isis is a strictly Islamist, brutal movement … the power and the leadership structure are clearly a male domain,” said Tophoven.

Messages between a British Isis fighter in Syria and his common-law wife, read in a British court last month, revealed that many fighters are taking several wives.

In an article in Foreign Policy focusing on Isis’s attitudes to women, former CIA analysts Aki Peritz and Tara Maller said fighters were committing horrific sexual violence on a seemingly industrial scale.

“For example, the United Nations last month estimated that (Isis) has forced some 1,500 women, teenage girls and boys into sexual slavery. Amnesty International released a blistering document noting that (Isis) abducts whole families in northern Iraq for sexual assault and worse.

Even in the first few days following the fall of Mosul in June, women’s rights activists reported multiple incidents of (Isis) fighters going door to door, kidnapping and raping Mosul’s women.” — Guardian News & Media