"The president has said that where we have some unique capabilities, he is willing to use those," he said during a Pentagon news conference on Thursday. "And in fact he has approved the use of armed Predators."
Two U.S. drones, armed with Hellfire missiles, carried out their first sortie on Thursday, but turned back because of bad weather, the vice chairman of the Joint Chiefs of Staff, Marine General James Cartwright, told journalists.
Gates said the United States was planning to send neither ground forces, nor military instructors to help Libyan rebels fight Gaddafi, saying that "there was never any lack of clarity about the limits on the U.S. role here."
"The United States has significant commitments in places other than the Middle East," he said.
The command of an international military operation against Gaddafi, initially led by the United States, was shifted to NATO in late March.
Despite dozens of flights carried out by NATO aircraft against Gaddafi's forces, the government troops maintain their combat capability and continue to pound poorly-equipped rebels with heavy artillery and rocket fire.