The three east London schoolgirls who fled the UK for Syria have joined a fearsome group of British female jihadis who run the lslamic State's ultra-religious police force, it has been reported.

Shamima Begum and Amira Abase, both 15, and Kadiza Sultana, 16, crossed over the Turkish-Syrian border last February and are believed to be living in the Syrian city of Raqqa.

Begum has forged social media links with three of the British leaders of the al-Khansa brigade – an all-women militia set up by the terror group a year ago – and it is understood the trio are now training with one of the notorious females arms of ISIS.

Covered in black from head-to-toe and wielding automatic weapons, the group has been accused of doling out savage beatings on the streets of Raqqa and spying on its citizens.

They are said to mercilessly patrol the streets of the terror group's adopted capital and has previously declared children as young as nine should be married, women should obey men – who are their masters – and remain 'hidden and veiled' at all times.

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Exodus: Amira Abase (left), 15, and Kadiza Sultana (right), 16, also travelled to Istanbul from UK on February 17 before reportedly entering Syria - where they could now be under the control of deadly female insurgents

Life of terror: 15-year-old Shamima Begum (pictured) - one of three British teenagers who is now believed to be inside Syria - contacted Aqsa Mahmood who is considered to be one of the leaders of brutal all-woman militant group al-Khansa

Extreme beliefs: The al-Khansa Brigade (pictured with automatic weapons) has said children as young as nine should be encouraged to marry and it is women's duty to obey men - who are their masters

Armed patrol: Chilling footage from inside ISIS' adopted capital Raqqa revealed how the notorious women of al-Khansa patrol the streets with automatic weapons - while tending to their toddlers

According to Syrian activist group Raqqa is being Slaughtered Silently, the female fanatics are feared by local women, particularly due to their use of torture.

The activist group claim imprisoned women are tortured using a device known as 'the biter', a iron bar with sharp jagged edges.

Placed on the helpless woman’s chest, the serrated edges of the bar are pressed into the woman's skin, causing deep lacerations.

Such is the violence of the torture, some women reportedly slip into unconsciousness due to the pain.

Aqsa Mahmoud, a 20-year-old woman from Glasgow who fled to Syria in 2013, is reportedly the leader of an al Khansaa group known as 'Om Amara'.

Om Amara is reportedly a female foreign battalion, with just two Arabic speakers who mercilessly patrol the streets of Raqqa.

Begum made contact with Mahmood, known as Umm Layth, on social media prior to departing for Turkey.

Begum also used her Twitter account to follow two other members of the al-Khansa brigade known only by their Islamic names Umm Khattab and Umm Waqqas.

In one of her recent tweets, Umm Waqqas advised British women on marriage in the Islamic State saying they should choose their jihadi fighters carefully and not to marry any 'Tom Dick or Harry'.

The British women jihadists in Syria have conducted a sustained recruitment campaign in the last few months and are thought to operate a woman-only jihadi route for European girls who are groomed to leave their Western lives for the caliphate.

They use social media, including Tumblr, Twitter and Ask.fm to publish detailed, practical advice about how to adapt to life in Islamic State and suggest essential items that the teenage wannabe-jihadists will find useful when they arrive.

Privately-educated Glaswegian Mahmood - along with Lewisham-born Khadijah Dare, 22 - are thought to be helping patrol Raqqa with guns and daggers hidden beneath their robes.

Terror leader: Aqsa Mahmood (pictured), who was reported missing by her Scottish parents in 2013, is now a prominent member of a dangerous all-woman police force that dishes out savage beatings on the streets of Raqqa, Syria

Shocking: In 2014, Aqsa Mahmood posted this photograph of her holding the severed head of a Syrian man executed for criminal acts in Syria as young children looked on

Trained to kill: One of the Halane twins, who fled to Syria to marry ISIS fighters, tweeted this picture with the caption: 'Fun day training for self defence in the Islamic State with humble sisters'

Wrong hands: The three teenagers who recently fled to Syria are feared to be with the al-Khansa Brigade, who have been accused of oppressively monitoring the behaviour of women in the city

The group operates as an ultra-oppressive police force monitoring the behaviour of females in the city and dishing out brutal punishments to anyone wearing shoes that aren't black, or those wearing veils made from the wrong material.

Mahmood recently advised that the Syrian winter was even colder than what she had experienced in her native Scotland and suggested 'winter woolies' were an essential.

Seventeen-year-old British jihadi twins Salma and Zahra Halane from Manchester, who left for Syria in June last year, are thought to be with older British women who have taken on matriarchal roles within the group.

They have been posting pictures on their Twitter accounts showing four al-Khansa women - veiled and armed with automatic weapons - undertaking 'self defence' training.

Umm Khattab started a Twitter account on June 27 - the day after Zahra and Salma Halane went missing from their home in Manchester to head for Syria.

Jihadi brides: Zahra and Salma Halane, 17, left their home in Chorlton, Manchester, to join the Al-Khansa Brigade in Syria in June last year - after becoming radicalised online

Shooting practice: One of the twins tweeted an image showing the women of Al-Khansa practising with their automatic weapons while dressed head-to-toe in black niqabs

Brain washed: The Halane twins have posted a number of pictures on their accounts where they are dressed completely in black and brandishing deadly weapons - just like their Al-Khansa sisters

Path of extremism: Yusra Hussein (pictured), 16, was also reported to have arrived in Syria in October and is also thought to have been mentored by British jihadists

She later tweeted: 'Missing twins – chilling with one of them now', adding she had met 'many British girls' since arriving in Syria.

The female branch of ISIS also released an eye-opening manifesto stating Western women who join the terror group have a duty to wed a jihadi – then spend their life cooking, cleaning and raising a family.

Two other British schoolgirls, Yusra Hussien, 16, from Bristol and Samya Dirie, 17, from south London, who were reported to have arrived in Syria last October, are also thought to have been mentored by the British jihadists.

Brutal patrols: The duties of the all-woman jihadi group include the strict enforcement of sharia law dress code as well as searching burka-clad women to ensure they are not enemy fighters in disguise

Jihadi bride: Another Briton who left Britain to join ISIS is Lewisham-born Khadijah Dare (left, with her Swedish terrorist husband Abu Bakr)

Muslim society: Members of the all-female Al-Khansa Brigade are seen walking in their adopted capital of Raqqa in Syria

Security services say that 600 British Muslims have gone to fight in Syria and around 60 of them are young women.

According to the Terrorism Research and Analysis Consortium, a US-based monitoring group, al-Khansa was set up by ISIS commanders in Raqqa, northern Syria, in February last year.

Its members dress in black robes, wear a full face veil and are paid a monthly salary of 25,000 Syrian pounds - about £100.

Their duties include the strict enforcement of sharia law dress code as well as searching burka-clad women to ensure they are not enemy fighters in disguise.

Uniform: Al-Khansa's members dress in black robes, wear a full face veil and are paid a monthly salary of 25,000 Syrian pounds - about £100

Deadly: British members of the female militant group are the most extreme members of the group and are responsible making barbaric threats against Britain

Mahmood, who once studied radiography at Glasgow Caledonian University, is regarded as one of the leaders of the group of British female jihadists.

She was reported missing by her parents over a year ago before surfacing in Syria last February as an outspoken supporter of the terrorist group.

In her tweets, she urged Muslim men and women who could not come to fight to instead commit terrorist atrocities at home, praising the brutal murder of Fusilier Lee Rigby in Woolwich, the bombing of the Boston Marathon and the shooting of soldiers at Fort Hood in Texas.