Syrians.
Syrians have been most of the insurgent leaders--not Iraqis. Foreign terrorists who don't give a darn about Iraq or Iraqis. Al Zarqawi is just one of several exploitive groups bringing death to others and exploiting Iraq's present circumstance.
The whole region exploits the Muslim faith and those who profess it to further their own ends. The region is treacherous. The stereotype is a largely deserved one.