Members of ISIS, including military leader and Georgian native, Abu Omar Al Shishani, centre, speaking at an unknown location between the Iraqi Nineveh province and the Syrian town of Al Hasakah. AFP
Members of ISIS, including military leader and Georgian native, Abu Omar Al Shishani, centre, speaking at an unknown location between the Iraqi Nineveh province and the Syrian town of Al Hasakah. AFP

Foreign fighters key to ISIS resurgence as thousands join new militias