U.S. President Barack Obama has approved the use of armed predator strikes in the western-led?military operation?against Libya,?U.S. Defense Secretary Robert Gates said at a new briefing on Thursday.?

The character of the armed predators in Libya has changed as Gaddafi's forces are digging in or "nestling up against crowded areas" to avoid being targeted by NATO aircraft, said Marine Corps Gen. James E. Cartwright, vice chairman of the Joint Chiefs of Staff, at the joint news briefing with Gates.

"The more-precise predators bring "their ability to get down lower and therefore, to be able to get better visibility, particularly on targets that have started to dig themselves into defensive positions," Cartwright said.

The aircraft are uniquely suited for urban areas where more traditional bombing can cause collateral damage, he added.

Two unmanned armed predators capable of around-the-clock coverage are now in Libya, the general said, adding that the first flights was launched?on Thursday?but were cancelled because of bad weather.

Previously the armed predators was used in Libya?"purely as intelligence, surveillance and reconnaissance systems," said Cartwright.?

Predator drones can fly surveillance missions and fire Hellfire missiles. They were widely used in Afghanistan, said Xinhua.

Although the United States has handed over command of the Libyan mission to NATO, it still provides some of the most critical capabilities in the conflict, such as aerial refueling, jamming, surveillance and certain ground attack capabilities, Xinhua reported.