Girls telephoned family from Syria and said: 'We're not coming back'

Last night their 44-year-old mother from Manchester said: 'I'm so shocked'

It is thought they may have joined one of their elder brothers in fight

Aged 16, they boarded a flight to Turkey and crossed the border into Syria

Salma and Zahra Halane were among top 20 students at their girls' school

Twin British schoolgirls who ran away to Syria were star pupils, with 28 GCSEs between them.

Salma and Zahra Halane were among the top 20 students at their girls’ school in Manchester but slipped out of their bedrooms and have fled abroad to become 'jihadi brides'.

The 16-year-olds, who disappeared two weeks ago, have telephoned their parents to tell them they have reached the war-torn country and warned them 'we're not coming back'.

Their mother told the Daily Mail last night: ‘I’m just so shocked.’ The 44-year-old, who wears a hijab, then broke down in tears at her semi-detached home in a leafy suburb of Chorlton, Manchester.

Police said today that the twins 'potentially pose a threat to themselves and the community'.

Scroll down for video

Star pupils: Twin British schoolgirls who ran away to Syria had 28 GCSEs between them. More recently the girls attended Manchester's Connell Sixth Form College, based at the East Manchester Academy (pictured)

The sisters may have followed their brother, who is thought to have flown out to fight with terror group ISIS last year.

Salma achieved 13 GCSEs, 11 of which were A*-C, while Zahra achieved 15 passes, 12 of which were A*-C grades - placing the girls within the top 10 per cent of their year group of 200 students.

The girls’ parents raised the alarm two weeks ago, after entering the twins’ room one morning to find their beds empty and passports and clothes missing.

The girls boarded a flight to Turkey from Manchester airport, and police alerted counter-terrorism colleagues in an attempt to trace the pair.

However, the twins – who have nine siblings, one of whom is a medical student – later contacted their parents to inform them they had crossed the border and reached war-torn Syria.

Officers are investigating how the girls funded their trip, over fears they may have been bankrolled by jihadi fighters who want them as their wives.

The North West Counter Terrorism Unit head Detective Chief Superintendent Tony Mole, said: 'First, I want to stress that the welfare of these two teenagers is our overarching priority.

'Two 16-year-old girls left the UK on June 26 and we believe that they have since entered Syria.

'At this stage we don't know for sure why they are there, or exactly who they are with.

'They are clearly posing a threat to themselves and potentially the community and their family and friends are concerned for their well-being.

'It is also important that we thank the community for their assistance in this matter while reminding them and the wider media that the family remain very concerned for the safety of their daughters'.

Extremists: Iraq and Syria are under threat from militants who fight under the banner of the Islamist group ISIS

The twins’ elder brother is already known to police in Greater Manchester, and is known to be abroad. Counter-terrorism officers plan to question him if he attempts to return to Britain.

The Halane family, originally from Somalia, have told friends and community leaders they are ‘absolutely devastated.’

Mohammed Shafiq, of the Ramadan Foundation, said: ‘The family is shocked and absolutely devastated, especially their mother.

‘Their son went to fight for ISIS about a year ago and has been over there since then. They believe he was radicalised over the internet.

'There has been an abject failure of intelligence agencies. How can two 16-year-old girls travel unaccompanied from Manchester Airport and arrive in Istanbul without any questions being asked?' - Mohammed Shafiq, Ramadan Foundation

‘The family were desperately unhappy to discover he had gone to Syria and they thought they were keeping a watchful eye on their other children ... and then this happens.

‘Their parents and brothers and sisters are desperately concerned for their safety and know they are in danger. It is extremely distressing for them. ‘

‘There has been an abject failure of intelligence agencies. How can two 16-year-old girls travel unaccompanied from Manchester Airport and arrive in Istanbul without any questions being asked?’

Shortly before their disappearance the girls were pictured attending an open day at their school, the newly-opened Connell Sixth Form College in Beswick, Manchester.

The girls’ father is known to pray at the Al Furqan Mosque in Moss Side, Manchester, but neither girls are thought to have attended.

Omar Barud, chairman of the mosque, said neither of the twins nor their mother had ever worshipped there.

‘We don’t support any form of extremism here and we have a very good relationship with the police,’ he said.

‘I wouldn’t want my daughter to travel to somewhere like Syria - at their age they should still be with their family, finishing their studies.'

Brits: Reyaad Khan from Cardiff (left) was also a promising student and appeared in this ISIS recruitment clip

Sources believe the two girls may have been radicalised over the internet using online forums to communicate with other like-minded teenagers.

They say the influence of an older brother, who they loved and respected and who had already left to fight jihad in Syria, ‘should not be under-estimated.’

The source said: ‘The whole thing may have been their brother’s idea and he may have facilitated the money for the tickets and they simply went along with it.

‘Obviously it is deeply troubling that teenage girls from backgrounds far removed from Syria are now being lured over there as jihadi brides.’

Mussurut Zia, general secretary of the Muslim Women’s Network UK, described what had happened to the girls as ‘religious grooming’ and said becoming a jihadi bride was not allowed in Islam.

She said: ‘The concept has probably been sold to the girls by people they may be in touch with through the process of recruiting. It may be they feel this is their personal role is this situation in Syria.

‘I see this as religious grooming. Because the girls are so young I doubt they will be able to make these decisions for themselves. They are going to be in awe of these people who are out there. They are probably older, they have the language, the rhetoric.’

A Greater Manchester Police spokesman said: ‘Greater Manchester Police is continuing to provide support to the family of two young girls, who were recently reported missing from their Manchester home, and are now believed to be abroad. At this stage, although the girls have made contact with their family we have no definitive evidence of exactly where the two girls are.’

The sisters have been described as 'quiet' and 'extremely religious'.

One neighbour said the girls were 'kept indoors' by their parents, although their brothers were allowed to come and go more freely.

A neighbour told The Sun: 'How do two young girls afford to fly out of the country without anyone stopping them?