I'm from your government, and I'm here to kill you.

LGM notes the euphemism "targeted killing" for the assassination of U.S. citizens deemed to be terrorists abroad:

... Anwar al-Awlaki is a US citizen allegedly engaged in inciting crimes against his fellow citizens and his government. Like any other US citizen, he is entitled to due process and a trial before the government could even consider whether he deserves the death penalty. When governments kill individuals outside such a judicial process, the terms for this are “summary execution” or “extrajudicial execution.” This is contrary to international human rights standards; international law makes no exception for states to derogate from such rules due to public emergency or internal unrest. When the US government targets its own citizens outside a judicial process it is also a violation of the US Constitution.

I think that's right, tho, even with my weak grasp of the laws of war, there seems to be some wiggle room.

If we're targeting a meeting which we believe Osama bin Laden will attend, and our intel shows that al-Awlaki is likely to be there, I don't think we have to cancel the attack because we might kill an American citizen. What seems to me prohibited is if we target the meeting because al-Awlaki is there.

Even then, however, what are the odds that al-Awlaki is not hanging on a regular basis with non-citizen terrorists, who could be "targeted" while al-Awlaki is "collateral damage"?