Al Qaeda-Linked Group in Syria Tightening Grip in North of the Country

Islamic State of Iraq and Syria (ISIS)

Gaziantep, Turkey (CNN) -- Al Qaeda has swept to power with the aim of imposing a strict Islamist ideology on Syrians across large swathes of Syria's rebel-held north, according to a CNN survey of towns, activists and analysts that reveals an alarming increase in al Qaeda-linked control in just the past month.

Al Qaeda-backed militants known as the Islamic State of Iraq and Syria (ISIS) are the predominant military force in northern Syria, according to activists and seasoned observers, and have a powerful influence over the majority of population centers in the rebel-held north.