The Obama administration insisted Friday that it has not and will not establish no-fly or "safe" zones over Syrian airspace, even though the Pentagon sternly warned Syria against flying in certain areas, and would even defend those zones if necessary.

"That is still off the table because of the implied military commitment that it would require in order to effectively enforce it," White House spokesman Josh Earnest replied when asked if President Obama has reconsidered his opposition in light of Syrian fighter jet aggression against U.S. troops.

"The concern is that while it sounds simple to maintain that kind of area, ultimately you're responsible for protecting the borders of that safe zone and then policing that safe zone once it's been created," he explained. "That would be work-intensive to say the least. It would be dangerous."

Doing so also "would likely require a greater U.S. military commitment. And all of that would come at the expense of our ongoing efforts to focus on degrading, ultimately destroying, ISIL," Earnest said.

On Monday, Pentagon spokesman Peter Cook also said there is not a no-fly zone above Syria. But he said Syrian "would be wise to avoid areas where coalition forces have been operating, and we will continue to defend them and if need be we will send aircraft again to defend our forces."