In general:

The majority of suicide bombings, attacks on civilian targets, and things like the mosque bombing are carried out by foreign fighters, often members of al Qaeda.

The majority of direct attacks on the U.S. and coalition, such as IEDs, mortars, and sniper fire, are carried out by local Iraqi insurgents.

The criminal gangs and militias are Iraqi for the most part, but the Sadr groups are supported by Iran to the tune of millions of dollars.

An older article on this here. I don't have more recent statistics handy, but I'm sure they're out there.

Your premise is somewhat flawed in that you are mushing terrorists and insurgents into one category. A lot of people do, on both sides of the issue. I don't.

I don't consider IEDs directed only at U.S. military targets to be terrorist attacks, for example. However bad they are for us, such attacks are still acts of war.