"The British women are some of the most zealous in imposing the IS laws in the region. I believe that's why at least four of them have been chosen to join the women police force." — British terrorism analyst Melanie Smith.

British female jihadists are now in charge of guarding as many as 3,000 non-Muslim Iraqi women and girls held captive as sex slaves.

Mujahidah Bint Usama published pictures of herself on Twitter holding a severed head while wearing a white doctor's jacket; alongside it, the message: "Dream job, a terrorist doc."

Great Britain is now the leading European source of female jihadists in Syria and Iraq.

As many as 60 Muslim women between the ages of 18 and 24 are believed to have left Britain to join the jihadist group Islamic State [IS] during the past twelve months alone, according to British terrorism analysts.

Dozens more have inquired about joining IS since the beheading of American journalist James Foley in Syria in August 2014 set off a frenzy of enthusiasm within jihadist circles.

Many of the women seem to be motivated by the hope of finding a jihadist husband, analysts say, apparently because they covet the cultural and religious "prestige" conferred upon Muslim widows whose husbands have died as "martyrs" for Allah.

Until recently, most of the British women affiliated with IS have been restricted to performing domestic chores such as cleaning and cooking. Lately, however, some women have become restive and have demanded a greater role in the IS enterprise.

Several British women are now engaged in IS recruiting efforts, using social media platforms such as Facebook and Twitter to encourage a new wave of British jihadists to travel to Syria and Iraq.

A half-dozen other women have been incorporated into a female-only militia called the Al-Khansaa brigade, based in the Syrian city of Raqqa, where the IS has set up its headquarters.

Al-Khansaa—named after a seventh-century female Arab poet who was a contemporary of the Muslim Prophet Mohammed—was established in February 2014 with the purpose of exposing male enemy jihadists who try to disguise themselves by wearing women's clothing in order to avoid detection and detention at IS checkpoints.

The brigade was also established to detain civilian women in Raqqa who do not follow the Islamic State's strict interpretation of Islamic Sharia law, including the requirement that all women be fully covered in public and that they be accompanied by a male chaperone.

In an interview with the blog "Syria Deeply," Abu Ahmad, an IS official in Raqqa, explained the rationale behind Al-Khansaa. He said:

"We have established the brigade to raise awareness of our religion among women, and to punish women who do not abide by the law. There are only women in this brigade, and we have given them their own facilities to prevent the mixture of men and women."

British terrorism analyst Melanie Smith told the Daily Telegraph that Al-Khansaa is a Sharia law police brigade whose social media accounts are run by British women and written in English.

"The British women are some of the most zealous in imposing the IS laws in the region," Smith said. "I believe that's why at least four of them have been chosen to join the women police force."

The Al-Khansaa brigade has now expanded its remit to operating brothels for the use of IS fighters. The result is that British female jihadists are now in charge of guarding as many as 3,000 non-Muslim Iraqi women and girls who are being held captive as sex slaves, according to British media.

"It is the British women who have risen to the top of the Islamic State's Sharia police and now they are in charge of this operation," another analyst told the Daily Mirror. "It is as bizarre as it is perverse."

A key figure in the Al-Khansaa brigade is said to be Aqsa Mahmood, a 20-year-old woman from Glasgow, Scotland who left for Syria in November 2013. Mahmood attended private schools and had wanted to become a doctor, but she dropped out of university without warning and vanished overnight in order to become a jihadist and marry an IS fighter.

Using the jihadist name of Umm Layth (Arabic for "Mother of the Lion") on Twitter (account now suspended), Mahmood has encouraged other British Muslim women to leave their families behind in order to join the jihad in Syria. She wrote:

"Biggest tip to sisters: don't take detours, take the quickest route, don't play around with your Hijrah [religious pilgrimage] by staying longer than 1 day for safety and get in touch with your contacts as soon as you reach your destination."

Mahmood, who says she is dedicated to the "pursuit of Allah's pleasure," added: "Once you arrive in the land of jihad, [IS] is your family."

In two tweets Mahmood described the kinship she felt with fellow Muslims in the Islamic State. Before referring to the place as "paradise," she concluded:

"Wallahi [I swear] I will never be able to do justice with words as to how this place makes me feel or what Ansaar of Shaam [helpers of Syria] have done for me and Allah only knows how much I love and appreciate these people for His sake..."

In another post, Mahmood called on Muslims to imitate those who murdered British soldier Lee Rigby outside the Woolwich Barracks in London in May 2013. "Follow the examples of your brothers from Woolwich, Texas and Boston," she wrote, referring also to the shooting in Fort Hood, Texas in November 2009 and the Boston Marathon bombings in April 2013.

Mahmood also called on Muslims to conduct jihad operations on British streets. In a recent tweet, she counselled: "If you cannot make it to the battlefield, then bring the battlefield to yourself."

She also wrote about martyrdom: "Allahu Akbar, there's no way to describe the feeling of sitting with the Akhawat [sisters] waiting on news of whose Husband has attained Shahadah [martyrdom]."

British media have published photographs of a burqa-clad Mahmood holding a shotgun, and of a child holding an AK-47 machine gun.

Mahmood's parents have said they cannot understand why their daughter ran away from home to become a jihadist:

"Our daughter was brought up with love and affection in a happy home, attended Craigholme private school, went to university and was always taught to show respect for mankind and was well integrated into this society. She may believe that the jihadists of ISIS are her new family but they are not and are simply using her. "If our daughter, who had all the chances and freedom in life, could become a bedroom radical, then it is possible for this to happen to any family."

Another British jihadist linked to the Al-Khansaa brigade, a 21-year-old medical student who goes by the name Mujahidah Bint Usama, published pictures of herself on Twitter holding a severed head while wearing a white doctor's jacket. The gruesome image appears alongside the message "Dream job, a terrorist doc," followed by images of smiley faces and love hearts.

Usama's Twitter account has now been suspended, but in her description of herself she wrote: "Running away from jihad will not save you from death. You can die as a coward or you can die as a martyr."

Yet another British jihadist, a 22-year-old convert to Islam named Khadijah Dare, has vowed to become the first female jihadist to execute a British or American captive.

Writing under the Twitter name Muhajirah fi Sham (Arabic for "immigrant in Syria"), Dare asked for links to video footage of the beheading of James Foley. In a slang-filled tweet she wrote:

"Any links 4 da execution of da journalist plz. Allahu Akbar. UK must b shaking up ha ha. I wna b da 1st UK woman 2 kill a UK or US terorrist!(sic)".

In another tweet, Dare wrote:

"All da people back in Dar ul kufr [land of disbelievers] what are you waiting for ... hurry up and join da caravan to where the laws of Allah is implemented. "No one from Lewisham [a borough in southeast London] has come here apart from an 18-year-old sister shame on all those people who afford fancy meals and clothes and do not make hijra [Mohamed's flight from Mecca to Medina in 622]. Shame on you."

Dare was born in London and converted to Islam at age 18, when she began worshipping at the Lewisham Islamic Center, a mosque linked to the radical cleric Abu Hamza and the two killers of Lee Rigby.

Dare moved to Syria in 2012 to marry a Swedish jihadist named Abu Bakr. The marriage was arranged through his mother on Facebook and she did not meet him until the day of their wedding. Dare recently published pictures of her son holding an AK-47 rifle.

In a Channel 4 documentary that aired in July 2013, Dare, who at that time went by the name Maryam, said:

"I couldn't find anyone in the UK who was willing to sacrifice their life in this world for the life in the hereafter... I prayed, and Allah ruled that I came here to marry Abu Bakr."

She also called on other British Muslims to join the jihad:

"You need to wake up and stop being scared of death...we know that there's heaven and hell. At the end of the day, Allah's going to question you. Instead of sitting down and focusing on your families or your study, you just need to wake up...."

On August 31, the Daily Mirror reported that Dare's jihadist rants have turned her into a "celebrity jihadi" who has become an "immense threat" due to her popularity. The newspaper reported that British security services have now made finding her a "top priority" over fears that radical Muslims are answering her calls to leave the UK to join IS in the Middle East.

In a four-minute video entitled, "Answering the Call–Foreign Fighters (Mujahedeen) in Syria," a burka-clad Dare appears firing an AK-47 rifle and pleading with fellow Brits to fight by her side in Syria. Speaking in a London accent, she said:

"These are your brothers and sisters as well and they need your help. So instead of sitting down and focusing on your families or focusing on your studies, you need to stop being selfish because time is ticking."

Not all British female jihadists are in their teens and twenties. A 45-year-old British convert to Islam named Sally Jones recently issued threats via Twitter to behead Christians. Jones, who changed her name to Umm Hussain al-Britani, wrote: "You Christians all need beheading with a nice blunt knife and stuck on the railings at Raqqa. Come here I'll do it for you!"

Police say Jones, who also goes by the name Sakinah Hussain, travelled to Syria in late 2013 after converting to Islam and developing an online romance with a 20-year-old British jihadist from Birmingham named Junaid Hussain.

Hussain, who uses the alias Abu Hussain al-Britani, was jailed in 2012 for running a computer hacking group known as Team Poison. He escaped to Syria in 2013 while on bail, and has been posting extremist messages on social media pledging to conquer the world and kill infidels.

Police fear Hussain is masterminding plan to teach jihadists how to empty the bank accounts of rich and famous Britons to fund terror attacks.

According to British media, Jones, originally from Kent in southeast England, was once an aspiring musician with an all-girl punk rock band but ended up spending a lifetime on social welfare benefits. She is now raising her 10-year-old son from a previous marriage as a Muslim under the Islamic State.

In an interview with The Sunday Times, Jones reflected on her new circumstances: "My son and I love life with the beheaders."