The teenage ‘terror twins’ who fled Britain to join ISIS have tried to recruit their younger siblings since arriving in Syria.

Twins Zahra and Salma Halane, from Manchester, sent threatening messages to their family, swearing hatred for ‘the infidels’ and encouraging them to join ISIS.

One message, sent by Zahra to encourage her two younger brothers to sign up as ‘future mujaheddin’, read: ‘We might seem evil to you, but we will all be happy in jannah [the afterlife].

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Fanatics: Salma (left) and Zahra Halane (right), who fled their homes in Manchester to become jihadi brides, attempted to recruit their whole family to join them in Syria using social media messages

‘Are you coming to Dawlah [ISIS]? They will train you up. You will meet boys from England, China, Ireland, Sweden, FROM EVERYWHERE. Want to see my Kalash [Kalashnikov]?? Ha ha ha.’

The now 17-year-old twins fled Manchester together in June last year, accompanied on their journey by an adult couple and an infant, to become jihadi brides.

Salma was married to a 19-year-old fighter from Coventry, whom she met online before travelling to join him.

The marriage was arranged by Aqsa Mahmood, a Glaswegian woman who was placed on a UN sanctions list last week.

Both their husbands have since been killed in battle, and Salma gave birth to a boy in June.

Concerns have been raised about a covert but rapidly growing network of recruiters and influence at the twins’ school.

Zahra added, in another message to her family: ‘We have a caliph and we must obey him. He said everyone that doesn’t come is kuffar [a non-believer]. I had to fulfil my commitment and so will you.

The now 17-year-old twins fled Manchester together in June last year, accompanied on their journey by an adult couple and an infant, to become jihadi brides

‘Allah, the merciful, placed something in mine and Salma’s hearts that we came to hate the infidels [in Britain] – to such a degree we could not even bear to look at them.

‘My best advice to you is to get the whole family to make hijrah [travel] to the Islamic State.’

The revelations have emerged in a new book about foreign jihadists by a Danish journalist, which is based on the testimony of friends and relatives.

The book, ‘Denmark’s Children in Holy War’, offers the most detailed account yet of how the girls, who had previously dreamed of being doctors and were dedicated Manchester United fans, were radicalised.

Written by terrorism expert Jakob Sheikh, of Politiken newspaper, the book portrays the sisters as well integrated members of Western society.

The Halane family is of Somali origin, but lived in Denmark as refugees before settling in Chorlton, in Manchester.

ISIS is using a complex web of recruiters to lure foreign girls to join them in Syria. More than 500 women from the west have left their lives behind and gone to join ISIS in Syria and Iraq

Once in ISIS, the women are likely to be sexually abused by the terrorists and used as sex slaves. Both the Halane twins were married to soldiers, but both their husbands have since died in battle

In December 2013, Salma was caught viewing ISIS propaganda at their sixth form college, which included images of a suicide vest, a boy with a machine gun and a British jihadist in Syria, named Abu Qaqa.

Qaqa, a prolific ISIS recruiter from Manchester whose real name is Raphael Hostey, later boasted of how he lured the twins to Syria.

The college did not alert the police at the time because she claimed that she was trying to find her older brother, who had previously travelled to Syria to fight.

Then, in June 2014, the twins stole £840 in cash from their father and fled their family home under cover of night.

They first flew to Istanbul in Turkey, with the couple and infant, where they posed as a family on holiday.

Later the twins, who have an older sister and seven brothers, crossed the Syrian border.