People trying to join Islamic State are using black market Syrian passports to enter the country through the Turkish border.

Smugglers have told Sky News it's difficult to know the true nationality of people crossing into Syria.

Counter-terrorism police say they believe three British schoolgirls missing from the UK have done just that.

Sky's Middle East reporter Tom Rayner managed to get hold of a blank passport in the Turkish border town of Akcakale (pron: Ack-chacker-lay).