NATO ships patrolled off Libya’s coast Wednesday as airstrikes, missiles, and energized rebels forced Muammar Qaddafi’s tanks to roll back from two key western cities. The Obama administration also said the United States was prepared to relinquish leadership of the campaign by the end of the week.

Qaddafi’s forces appeared to weaken in the western region that has been his stronghold, and diplomats neared an agreement to let NATO assume responsibility for the no-fly zone.

Defense Secretary Robert Gates said the United States could relinquish control as soon as Saturday. He had no answer when asked about a possible stalemate if Qaddafi hunkers down, and the coalition lacks UN authorization to target him.

Rear Adm. Gerard Hueber, a top U.S. officer in the campaign in Libya, said the international forces were attacking government troops that have been storming population centers. The coalition’s targets included Qaddafi’s mechanized forces, his artillery, and mobile missile sites, as well as ammunition and other military supplies.

A doctor in Misrata said the tanks fled after the airstrikes, giving a much-needed reprieve to the city, which is inaccessible to human rights monitors or journalists. He said pro-Qaddafi snipers continued to fire on civilians from rooftops on Wednesday.

In Zintan, a resident said Qaddafi’s forces were at the base of a nearby mountain and were shelling in that area, but rebels forced their retreat from all but one side of the city.

In the east, pro-Qaddafi troops who have besieged Ajdabiya attacked a few hundred rebels on the outskirts Wednesday. The rebels fired back with Katyusha rockets but have found themselves outgunned. Plumes of smoke rose over the city, which is 95 miles south of the de-facto rebel capital of Benghazi.

Neither the rebels nor Qaddafi has mustered the force for an outright victory, raising concerns of a prolonged conflict

In Benghazi, the rebel council named Mahmoud Jibril, a U.S.-educated planning expert who defected from the Qaddafi regime, the leader of the governing body, according to rebel spokeswoman Iman Bughaigis.

Qaddafi’s regime has alleged that dozens of civilians in Tripoli have been killed in the international bombardment, but the Pentagon said there was no evidence of that.

The Associated Press contributed to this report.