During the Libyan revolution, U.S. drones were a significant part of the NATO forces involved, carrying out nearly 150 attacks. But when the conflict ended, the drones stayed. CNN reported in June:

“A senior Libyan official told CNN that the U.S. is flying surveillance missions with drones over suspected jihadist training camps in eastern Libya because of concerns over rising activity by al Qaeda and like-minded groups in the region but said that to the best of his knowledge, they had not been used to fire missiles at militant tra

Following yesterday’s attack in Benghazi that killed U.S. Ambassador Chris Stevens and three other Americans, President Obama declared that the killers would be found and that “justice will be done.”

CNN reported today on the military role in that "justice:"

The Pentagon dispatched a contingent of Marines to Libya, moved warships toward its coast, and planned to use drones in a stepped up search for those responsible for an attack on a U.S. consulate that killed the American ambassador and three others.”

A “senior military official” provided more details on the planned use of drones

“American drones also were expected to join the hunt for potential targets. They would be part of "a stepped-up, more focused search" for a particular insurgent cell that may have been behind the attack, the official said. The unmanned surveillance aircraft are expected to fly over Benghazi and other areas of eastern Libya to look for militant encampments.”

And, while the reports now are only of surveillance, an educated guess would suggest that the drones are (or soon will be) armed, and that missiles will likely be fired.