LONDON: Sixty British women and girls, including 18 teenagers, are believed to have travelled to war-torn Syria to join Islamic State militants, the UK 's top counter-terrorism police officer said today.Deputy assistant commissioner Helen Ball, senior national coordinator for counter-terrorism, said that about five of them are 15 - 16.The figures came as fresh CCTV images emerged of three London schoolgirls who secretly caught a flight to Istanbul after slipping out of their homes last month.Shamima Begum, 15, was pictured with Amira Abase, also 15, and Kadiza Sultana, 16, on the Turkish leg of their trip before they were feared to have crossed the border into Syria.On 24 February, a week after the girls left their homes, Scotland Yard said they were believed to have entered Syria.It is thought they were smuggled into the country, large swaths of which are controlled by IS, near the Kilis border crossing.Ball said police were getting increasingly concerned about the growing trend of young women planning to make the treacherous journey from Britain - many of whom are disguised to avoid suspicion."This is a growing problem and it's one of real concern. The more everybody involved in travel can be alert and be vigilant and look out for people the better," she told BBC."There's a new police power to remove someone's passport if we are concerned they might be travelling for terrorist activity - we have used that already."But mostly this is about vigilance of everyone who is working in the industry .... some of those women and girls are very carefully prepared for their travel so that they don't stand out. They take unusual routes and it is very hard to spot them," Ball said.Turkish Airlines and UK border agencies have been criticised for failing to stop the three girls from travelling on a now well-worn route to IS in Syria.