CCTV images captured last month showed three Bethnal Green Academy girls — Shamima Begum and Amira Abase, both 15, and Kadiza Sultana, 16 — on the Turkish leg of what is believed to have been their journey to join the IS in Syria, BBC reported.
According to the report, the three girls flew from London to Istanbul on February 17 and the CCTV images showed the girls waiting at Bayrampasa bus station in Istanbul later that day.
Scotland Yard believes that the girls are now in Syria.
The BBC understands that the girls waited at the bus station before travelling to Urfa, close to the Syrian border, on February 18.
From there, they are thought to have been driven to a border crossing point by human traffickers. After that the teenagers apparently crossed over into Syria.
A group of waiting IS men “immediately picked them up in cars”, said a human trafficker, who facilitated the girls’ movement to Syria’s border with Turkey.
The girls had flown from London’s Gatwick Airport to Turkey after telling their parents that they were going out for the day.
The girls’ families have made a number of emotional appeals for them to return home.
Police have revealed that about 60 women and girls were now thought to have travelled from Britain to Syria — including about 22 last year.
“When I say young, all but four of those 22 were aged 20 or younger,” Deputy Assistant Commissioner Helen Ball, Britain’s senior national co-ordinator of counter-terrorism, told BBC.
“The last five who have travelled were aged 15 and 16, so this is a growing problem and it is one of real concern.”
The Syrian civil war has had a “galvanising” effect on people becoming radicalised, she said.
Kalsoom Bashir, co-director of the counter-extremism organisation Inspire, said it was “shocking but not surprising” that young girls were being lured to Syria.
She said the IS had a “very specific campaign” to target young and vulnerable women, saying here was a growing trend of women who were getting “younger and younger”.
Girls such as Shamima, Amira and Kadiza were victims of “ideological grooming” by the IS, she added.