The search for three London schoolgirls thought to be travelling to Syria to join Islamic State (IS), has refocused attention on the women and girls who are said to have left the UK to join IS.

Kadiza Sultana, Shamima Begum and Amira Abase flew to Turkey from Gatwick on Tuesday.

The BBC spoke to a people smuggler who explained how foreign women who wish to join IS are able to cross the Turkish border into Syria.