The existing conventions do not prohibit attacking militants while they are in the middle of civilians, even if they are not doing that as part of some hostage/human shield operation. It may be considered morally not ok, but doing so does not violate any obligation.
That's not exactly true; it would depend on how you attacked the combatants, and how much collateral damage you caused. Civilian casualties must be proportionate to the military value of the target.
Reporting is still coming in on these attacks so virtually every comment on these huge long threads could end up falsified one way or the other, but from what I can tell, it looks like these attacks will not only clear that bar, but that they'll do so in a way unprecedented in the history of modern warfare. But we'll see!
