The family of British woman suspected of encouraging three London schoolgirls to join the Islamic State in Syria said that officials “failed” to stop them from leaving the country.

Shamima Begun, 15, and Kadiza Sultana, 16, and another girl reportedly joined Aqsa Mahmood, 20, in the country riddled by ISIS oppression. Mahmood, who reportedly went to Syria to be a “jihadi bride” in 2013, had online contact with one of the girls last week before they left the country.

Mahmood’s family said in a statement that it was “full of horror and anger” that she “may have had a role to play” in recruiting the girls for the terror group.

"Aqsa's social media has been monitored since she disappeared over a year ago, yet despite alleged contact between the girls and Aqsa, they failed to stop them from leaving the UK to Turkey, a staging post for Syria."

The family’s lawyer told BBC that they want to know how the woman could have traveled to Turkey alone.

The three girls are close friends at Bethnal Green Academy in east London. They were last seen Tuesday morning after they left home, saying they were going out for the day.

But surveillance video revealed the girls traveled to London’s Gatwick airport and boarded a Turkish Airlines flight which landed in Istanbul Tuesday evening.

Police say the girls are close friends with another 15-year-old girl who fled to Syria in December.

"We are concerned about the numbers of girls and young women who have or are intending to travel to the part of Syria that is controlled by the terrorist group calling themselves Islamic State," Metropolitan Police Commander Richard Walton told Sky News.

"It is an extremely dangerous place and we have seen reports of what life is like for them and how restricted their lives become. It is not uncommon for girls or women to be prevented from being allowed out of their houses or if allowed out, only when accompanied by a guardian,” Walton told reporters.

Security checks for people departing from U.K. airports make it a "walk in the park for jihadis and girls like this" to leave, Former Metropolitan Police border control officer Chris Hobbs says.

"At the moment you go through security, you get on the plane, you might be checked by a private security guard," he said. “If you're on a watch list then you will ping the system. If you're not on the radar then the odds are you will get on the plane without too many problems."

The girls-- who are British nationals of Bangladeshi descent-- were all wearing Western clothes at the airport. Shamima was wearing black glasses and a hijab, Kadiza was also wearing glasses and a grey striped scarf, and the unidentified girl was wearing glasses and a black head scarf. 

"The choice of returning home from Syria is often taken away from those under the control of Islamic State, leaving their families in the U.K. devastated and with very few options to secure their safe return," Walton said.

The number of Westerners who have travelled to Iraq and Syria to join ISIS is thought to be about 3,000, including as many as 550 women, according to the London-based Institute for Strategic Dialogue.

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