Editor's note: Mary Ellen O'Connell holds the Robert and Marion Short Chair in Law and is research professor of international dispute resolution at the Kroc Institute for Peace Studies at the University of Notre Dame. She is a specialist on the international law of armed conflict and is the author of "The Power and Purpose of International Law" (Oxford University Press, 2008). She has been a professional military educator for the U.S. Department of Defense, chaired the Use of Force Committee of the International Law Association (2005-2010) and is a vice president of the American Society of International Law.
(CNN) -- Harold Koh, legal adviser to the U.S. State Department, attempted to convince Congress on June 15 that the "limited nature" of U.S. military operations in Libya are not "hostilities" as envisioned in the War Powers Resolution, and, therefore, required no Congressional authorization.
But the U.S. had better be involved in hostilities or else our forces are engaged in unlawful killing. The U.S. has deployed manned and unmanned aircraft to fire missiles and drop bombs -- the type of weapons only permissible for use in armed conflict hostilities.
Most U.S. attacks in Libya today reportedly are being carried out by unmanned Predators. President Obama's report to Congress, also delivered on June 15, tries to minimize the meaning of using Predators. The report refers to "occasional strikes by unmanned Predator UAVs." But armed Predators carry two Hellfire missiles.
Missiles and bombs are permissible for use in hostilities because the intensity of fighting supports a presumption that killing without warning or attempt to capture is justified. Moreover, during hostilities, the law tolerates the unintended deaths of civilians as long as the number of those deaths is not disproportionate to the value of the military objective.
Outside of hostilities, where peacetime law enforcement rules govern the use of lethal force, killing is justified to save a human life immediately. "Collateral" deaths are not tolerated.
In a CNN Opinion post of April 25 I wrote, "President Barack Obama uses (drones) in places where, for political reasons, he does not want a significant U.S. military presence. Yet, that is the fatal attraction of drones -- they may not seem like a weapon of war, but they are."
I also wrote the U.S. was not likely to accomplish its goals in Libya with drones. It is still not entirely clear what the goals in Libya are. Whatever the goals are, the president is now projecting costs of over a $1 billion for the Libya operation through the end of September.
And for this the administration's lawyers are pushing strained interpretations of the law to keep the U.S. in the fight without Congressional authorization.
Others have looked at the contradiction between Koh's academic positions on the importance of the Congressional role in decisions to go to war and his position today. I wish to point to his appropriate and heavy criticism of Bush administration lawyers who manipulated or ignored international law in order to justify unlawful techniques of interrogation. He particularly criticized the "narrow" definition of torture, which he said, "flies in the face of the plain meaning of the term."
In addition to torture, international law defines "armed conflict" and "hostilities":
"The term 'hostilities' is another term closely related to the concept of 'armed conflict.' The (International Committee of the Red Cross) ... defines the term as 'the (collective) resort by the parties to the conflict to means and methods of injuring the enemy.' The term refers to the actual fighting of an armed conflict."
Koh should be very familiar with this definition. Not only was it identified by 18 of the leading scholars on the law of war, it has been posted on the website of the International Law Association since August 2010. The report that includes it forms the basis of my critical analysis of U.S. drone use that, in a public forum, Harold Koh acknowledged he had read.
The international law definition of hostilities comports with common sense. As Sen. Dick Durbin, D-Illinois, put it on "Meet the Press" last weekend: "It doesn't pass a straight-face test in my view that we're not in the midst of hostilities (in Libya)."
The opinions expressed in this commentary are solely those of Mary Ellen O'Connell.