They also battled to loosen the grip of rebels on two cities close to Tripoli. But in at least one case, their tactics appeared to lead them into a trap.

Residents said pro-Gadhafi troops punched into the city of Misrata, 200 kilometers east of Tripoli, the capital, with mortars and tanks but were pushed out five hours later by rebel forces. The rebel commanders intentionally opened the way for government tanks to enter the city, then surrounded them and attacked with anti-aircraft guns and mortars, said Abdel Fatah al-Misrati, one of the rebels.

"Our spirits are high," al-Misrati said. "The regime is struggling and what is happening is a desperate attempt to survive and crush the opposition. But the rebels are in control of the city."

Sunday's fighting appeared to signal the start of a new phase in the conflict, with Gadhafi's regime unleashing its air power on the rebel force trying to oust the ruler of 41 years.

AP