Armed US Predator drones are carrying out missions over Libya, Defence Secretary Robert Gates has said.
Mr Gates said their use had been authorised by President Barack Obama and would give "precision capability" to the military operation.
US drones are already used to target militants along the Pakistan-Afghanistan border.
Libyan rebels have been battling Col Gaddafi's troops since February but have recently made little headway.
"President Obama has said that where we have some unique capabilities, he is willing to use those," Mr Gates told a news conference.
He said two armed, unmanned Predators were being made available to Nato as needed, and marked a "modest contribution" to the military operations.
Mr Gates denied that the drone deployment was evidence of "mission creep" in Libya and said there were still no plans to put US "boots on the ground" in Libya.