Police fear a mother and her four children are bound for Syria after going missing from their London home.
Zahera Tariq, 33, is believed to have flown with her three sons and daughter from London City Airport to Amsterdam on Tuesday.
She was last seen at her home address in Wathamstow on that morning, the Metropolitan Police said.
Today the force released CCTV images of the family - including three boys aged 12, 11 and four and a nine-year-old girl - as they launched an international search for them before they reach Syria.
Commander Richard Walton, from the Met's Counter Terrorism Command, said: "We're concerned about Zahera and her four children and we're doing all we can to work with our partners and colleagues both here and abroad to try and locate them and make sure they are all safe and well.
"Whilst we do have some concerns that Zahera may be thinking of travelling to Syria, there is no current information to suggest that she's already travelled there.
"Her family are extremely worried about her and her three sons and daughter and we would urge anybody with information to contact us as soon as possible."
Zahera is described as an Asian woman of medium build, approximately 5ft 3ins tall, with long black hair, the Met said.
Her oldest son, Muhammad is 12 years old, of medium build, approximately 5ft tall and has medium-length black hair.
Amaar, 11, is said to be skinny with medium-length black hair. Her daughter, Safiyyah, is nine years old, of skinny build and long black hair.
Her youngest son, Aadid, is four years old and has black hair.
Several cases have recently emerged where women and children from the UK are feared to have gone to parts of Syria controlled by the so-called Islamic State.
In July it was reported that several members of the same family from Luton, including three children, were believed to have travelled to Syria after a holiday in Bangladesh.
Scotland Yard recently confirmed that it believed more than 40 women and girls had travelled to Syria from Britain in the last year.
The Met urged anyone with information regarding Zahera and her children's whereabouts to call the Anti-Terrorist Hotline on 0800 789 321.
