Women are the new target for recruitment for the Islamic State (IS), with researchers seeing "unprecedented" calls for fighters to marry British and European women.
The women, some just teenagers, are bombarding IS fighters with marriage proposals during social media 'Q&As' and researchers estimate as many as 50, most of them British, could have already gone to join fighters in Syria and Iraq.
Four women from the UK have been identified by experts for the first time this week, though they are believed to have been in Syria together since early this year and tweet in English from the country.
"We found a gang of four girls who appear to be living near each other in Raqqa [an IS stronghold which is the town closest to where US journalist James Foley was beheaded]," said Melanie Smith, a research associate at the International Centre for the Study of Radicalisation (ICSR), King's College, who monitors the recruitment of women by Islamic State, formerly known as ISIS.
"Usually, it is hard to tell if they are British, if they tweet in English, but these girls were using particularly British slang. We don't know where they are from but they have been there since around February, and they don't appear to have known each other before they went out.
"Typically, the women who are out there tend to form clusters, they might be married to Isis fighters in the same unit."
When the first calls were issued by rebel fighters for Muslims to come to Syria, women were explicitly told not to come, according to Shiraz Maher, Senior Fellow at the ICSR.
"The exception has been Isis," he said. "Particularly since the declaration of the 'Caliphate', there has been an encouragement for everyone to come, along those who are particularly asking women to come are still the minority."
For the fighters to build "a functioning state", women who are loyal to the cause and ready to endure the obvious hardship of being in a war-torn land are crucial, Maher said. "There's been specific calls for doctors, engineers, lawyers to come to the 'Caliphate', and for a state to function, women need to come, they need to have children."
At the moment, researchers do not believe any of the women are actually fighting alongside the male jihadists, but Smith said that "that could change". A few local women are however fighting against Isis for the Kurdish Peshmerga forces.
"There are pictures of them with an AK47 or in tanks but so far we think that's more of a status symbol," Smith told HuffPost UK.
"Sunni jihadis have never called on women to fight, they come to be the home-front, to cook, clean and offer logistical support. They are almost all married to Isis fighters," Maher said.
And because most of the women want to be married before they take the step of going to Syria, it has led to a massive demand for matchmaking over social media.
"This is completely unique to this conflict, it is unprecedented to see girls posting requests on websites like Ask.fm to ask fighters to marry them so they can be 'part of this'," Maher said. "We've never seen that before, though we've never seen social media used to such an extent in conflict before.
"All the questions to the fighter on Twitter or Ask.fm are things like 'do any of the fighters want to get married?', 'can you arrange for a man to marry me in Turkey, so I can come over?'. But it shows us that all though there are a lot of them talking about it on social media, many aren't making that final step of going out there."
So who are some of the dozens of British women who have joined the Islamic State?