U.S. Defense Secretary Robert Gates said it will be up to Libyans to determine their future, stressing the limits of U.S. involvement in what threatens to become a protracted civil war.

Gates arrived in Libya's neighbor Egypt as Western warplanes pounded Muammar Gaddafi's forces for the fifth night in a row. Gates, who had been a voice of caution in Washington in the run-up to military action in Libya, was in Cairo after a two-day trip to Russia that threw a spotlight on anxiety over coalition strikes on Gaddafi's air defenses and artillery.

Russia, China, India, Brazil and other developing countries have condemned air strikes as risky and unwarranted.

In Cairo, one Egyptian reporter drew comparisons to the 2003 Iraq invasion, which Gates swiftly rejected. Another journalist asked whether he would consider outside mediation to end the conflict, a possibility he dismissed.

"It seems to me that if there is a mediation to be done ... it is among the Libyans themselves. This matter at the end of the day is going to have to be settled by Libyans," Gates said. "It's their country."