Earlier quoted context omitted.
Question is are you in a state of war? Are these considered casualties of war? If yes, then execution without trial is a given.
Last I looked the US weren't at war with Pakistan.
The US haven't formally been at war with anyone since WWII[1], so we must rely on an informal definition of war (otherwise even Vietnam would be excluded).
A middle-ground definition of war that requires parties to be nation states but doesn't require a declaration of war, seems a bit arbitrary.
Instead of declaring war, the US now has Congress-sanctioned "use of military force". This includes the current "conflict" with the Taliban regime.
In this context the line between war casualties and assassination is very blurry. I think the blur itself might be one of the worst things about this new way of waging war.
[1] http://www.theatlantic.com/politics/archive/2013/08/all-the-...