Image from video released by ISIS on 4 January 2014
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Who are the ISIS militants?

James Robbins explains the background and aims of the Islamic State of Iraq and Al-Shams (ISIS)

As concerns continue about the situation in Iraq where the Islamic State of Iraq and Al-Shams (ISIS) has taken control of several cities, the BBC's James Robbins looks at who the fighters are who make up ISIS and what their aims are.