London: British counter-terrorism officers have been accused of failing to take basic steps to prevent young women from joining Daesh after three London schoolgirls evaded authorities to travel to Syria.

One of the missing girls, Shamima Begum, 15, is thought to have made online contact with a Scottish woman who left Britain to marry a Daesh fighter in 2013. The contact with Aqsa Mahmood, whose social media use is supposedly under surveillance by counterterror agencies, came two days before Begum slipped out of her East London home and met up with school friends Kadiza Sultana, 16, and Amira Abase, 15.

On 17 February, the three girls secretly made their way to Gatwick airport and caught a Turkish Airlines flight to Istanbul, Turkey, from where they are feared to be heading towards Islamic State-held territory in Syria. A Twitter account thought to be linked to Begum shows that she contacted Mahmood, a prominent online advocate of Daesh, on February 15, saying: “follow me so I can dm you back”.

Aamer Anwar, a lawyer for Mahmood’s family, said on Sunday they were “incredulous” that the contact could go unnoticed by Scotland Yard and other counterterror agencies. “We are aware from contact with Special Branch and the police that her social media contact is regularly checked and regularly monitored,” he told the BBC. “The idea that a young 15-year-old should make contact with Aqsa, who’s regarded as a terrorist, yet no action is taken, the family of that young girl do not have the customary knock on the front door.

“The fact that these three girls manage to reach the airport — the common sense approach of Special Branch at the airport, the UK border agencies, don’t notice the fact that two 15-year-olds [and] a 16-year-old are unaccompanied, going on a flight to Turkey, the staging post to Syria which is what Aqsa did herself and they aren’t stopped.

“Obviously the family are deeply distressed and angry and they want answers because they’re thinking how many other families is this happening to.”

Scotland Yard said on Friday that it had interviewed the three missing girls in December after one of their 15-year-old school friends boarded a flight to Turkey in a bid to join Daesh militants. The four were all students at the Bethnal Green Academy school in East London.

However, officers said interviews were part of a routine inquiry and that the three were not put under any kind of surveillance. “There was nothing to suggest at the time that the girls themselves were at risk and indeed their disappearance has come as a great surprise, not least to their own families,” a Scotland Yard spokesman said.

Detectives are investigating whether the girls have been in contact with their school friend in an effort to cross the Turkish border into Syria. They are working closely with Turkish authorities in the hope that the snowy conditions in Istanbul may have disrupted their travel overland

On Saturday night, the families of the three girls issued emotional appeals for them to return home. Begum’s family said: “We miss you terribly and are extremely worried about you. Please, if you hear this message, get in touch and let us know you are safe. We want you home with us. You belong at home with us. Syria is a dangerous place and we don’t want you to go there. Get in touch with the police and they will help to bring you home. You are not in any trouble.

“We understand you have strong feelings and want to help those you believe are suffering in Syria. You can help from home, you don’t have to put yourself in danger.”

Kadiza’s family released a similar statement, which said: “We are not angry with you and you have not done anything wrong. We miss you terribly, especially Mum, and things have not been the same without you.”

Amira’s family named the missing girl for the first time in a statement in which they also appealed for her to return home.

The Abase family said: “Amira, we miss you so much, everyone, your family and your friends.

“We want you to come home as soon as possible; all we are hoping for is you to come home safe, we love you so much.

“Please come home Amira, everyone is missing you. You are strong, smart, beautiful and we are hoping you will make the right decision.

“We miss you more that you can imagine. We are worried and we want you to think about what you have left behind.”

Conservative MP Sarah Wollaston, the chair of the Commons health committee, said she had “no sympathy for so-called A-grade girls travelling to Syria without doing their homework on IS [Daesh] rape & murder of women”. She called for strict measures at the border to prevent under-18s from flying to Turkey without parental consent.

On Twitter, she said: “Joining IS knowingly colludes with their grotesque mass murders, torture, enforced slavery & rape.”