It is feared that three missing London schoolgirls may be travelling through Turkey to Syria to join Islamic State (Isis), the Metropolitan Police said.
Shamima Begum, 15, Kadiza Sultana, 16, and an unnamed 15-year-old, who are all pupils at Bethnal Green Academy, flew from Gatwick to Istanbul on Tuesday (17 February) during their half-term break, said police in a statement.
None told their families that they were travelling to Turkey, and gave them plausible reasons why they would be away for the day.
Counter Terrorism Command Commander Richard Walton said: "We are extremely concerned for the safety of these young girls and would urge anyone with information to come forward and speak to police. Our priority is the safe return of these girls to their families.
"We are reaching out to the girls using the Turkish media and social media in the hope that Shamima, Kadiza and their friend hear our messages, hear our concerns for their safety and have the courage to return now, back to their families who are so worried about them."
Several British girls and women have travelled to Syria to join IS, which controls huge areas of Syria and Iraq.
Last year, Manchester teenage sisters Zahra and Salma Halane travelled from their home in Manchester to join IS in Syria, where they married jihadist fighters who were subsequently killed.
The star pupils, who aspired to become doctors, are believed to have travelled to Syria to join their brother, an IS fighter.
In December, police stopped a 15-year-old girl from Tower Hamlets, London, who planned to join IS, stopping her Istanbul-bound plane on the runway just before it took off after receiving a tip-off.
Walton added: "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.
"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.
"The choice of returning home from Syria is often taken away from those under the control of Islamic State, leaving their families in the UK devastated and with very few options to secure their safe return.
"If we are able to locate these girls whilst they are still in Turkey, we have a good possibility of being able to bring them home to their families."
Police said Shamina is 5ft 7in tall, and wearing black thick rimmed glasses, a black hijab, light brown and black leopard print scarf, dark red jumper, black trousers and jacket, carrying a dark blue cylindrical shape holdall with white straps.
Kadiza is 5ft 6in tall, of slim build and wearing black-rimmed glasses, a long black jacket with a hood, grey striped scarf, grey jumper, dark red trousers, carrying a black holdall.
Both are British nationals, speak English with London accents and also speak Bengali.
The third girl is 5ft 6in, of slim build, wearing black thick rimmed glasses, black head scarf, long dark green jacket with fur lined hood, light yellow long sleeved top, black trousers, white trainers and carrying a black Nike holdall. She speaks English.
Anyone with any information on the girls' whereabouts should call the free phone Anti-Terrorist Hotline number on 0800 789 321.