From and NYT article discussing a Libyan no-fly zone:
Even so, the opening mission of imposing a no-fly zone would almost certainly include missile attacks on air defense sites of a sovereign nation, which some would indeed regard as an act of war.
Some? Some would regard this as an act of war? I’m pretty sure that if another nation launched missile attacks on American air defense sites more than just “some” of us would consider it an act of war. That’s not to say a no fly zone isn’t the answer, but let’s agree to call a spade a spade.