Defense Secretary Robert Gates said Tuesday that Libyan military command centers "wherever we find them" are legitimate targets for U.S. and NATO air attack, suggesting that strongman Muammar al-Qaddafi himself is increasingly in danger.

NATO planes are "not targeting him specifically," but will continue to take aim at his command centers, Gates said. That distinction is exceedingly thin, given that Qaddafi is commander in chief of government forces using brute force against civilians seeking to overthrow him. On Monday, NATO bombs turned sections of his Tripoli headquarters into smoldering ruins.

A Libyan government spokesman denounced Monday's bombing as a failed assassination attempt.

Gates and British Defense Minister Liam Fox, speaking to reporters at the Pentagon after a meeting that included Adm. Mike Mullen, the top ranking U.S. military officer, indicated that facilities from which Libyan leaders command their forces will remain at risk.

"We consider them legitimate targets," Gates said. "We are not targeting him specifically, but we do consider command and control targets to be legitimate targets wherever we find them."

Although Gates said such targets have been considered legitimate from the beginning of the NATO-led air campaign more than one month ago, the initial bombing focus was on Qaddafi's air defenses, supply depots and maneuvering ground forces -- particularly those in the east that have clashed repeatedly with rebel forces and those in the western port city of Misrata.

Now NATO is attempting to ratchet up pressure on Qaddafi and those in his inner circle by holding at risk his command centers as well as related structures that enable the regime to exercise power. A separate airstrike in Tripoli n Monday hit Libyan TV and temporarily knocked it off the air.

This appears to represent an evolution of the air campaign, which is adjusting its targeting priorities as Libyan forces have adapted to weeks of airstrikes on ground forces, the imposition of a no-fly zone and persistent rebel assaults in several key areas.

Gates said Libyan military command centers in Tripoli and elsewhere are legitimate targets under the U.N. Security Council resolution that authorized the use of force -- short of inserting an occupying ground force -- to protect civilians from attacks by the Libyan government.

"Those (command) centers are the ones that are commanding the forces that are committing some of these violations of humanitarians rights, such as in Misrata," Gates said.

In his remarks, Fox alluded in vague terms to this evolution, saying he, Gates and Mullen had discussed how to "exploit emerging opportunities on the ground" in Libya, mentioning the U.S. decision last week to add armed Predator drone aircraft to the mix of NATO aircraft attacking targets in urban settings.

"There is little doubt across the alliance that this key contribution has proven to be of immense value protecting civilians in Misrata and have helped opposition forces to defend themselves against this brutal regime there," Fox said. Later he asserted, "The regime is on the back foot," and that the sooner Qaddafi "recognizes that the game is up," the better for all.