According to Time magazine,

Pentagon officials have been saying for some time that Iraqis must take more responsibility for securing their country. But can these local forces protect its critical infrastructure without U.S. help? Top American officials disagree, and that has caused friction between the State and Defense departments and may complicate the planned reduction of U.S. troops.

The State Department's top official in Iraq, Ambassador Zalmay Khalilzad, argues vigorously that the U.S. needs to maintain a robust military presence around areas such as oil pipelines and power grids, targeted by the insurgents.

A Washington Post piece a month ago indicated similar friction.