RAS LANOUF, Libya – Western air raids targeted Moammar Gadhafi's hometown of Sirte for the first time Sunday night as rebels quickly closed in on the city to overcome a formidable obstacle to reach the capital Tripoli.

A heavy bombardment of Tripoli also began after nightfall, with at least nine loud explosions and anti-aircraft fire heard.

Earlier in the day, rebels regained two key oil complexes along the coastal highway that runs from the opposition-held eastern half of the country toward Sirte and beyond that, to the capital.

Moving quickly westward, the advance retraced their steps in the first rebel march toward the capital. But this time, the world's most powerful air forces have eased the way by pounding Gadhafi's military assets for the past week.

Sirte is strategically located about halfway between the rebel-held east and the Gadhafi-controlled west along the Mediterranean coast. If the rebels could somehow overcome Sirte, momentum for a march on the capital would skyrocket.

The Gadhafi authrities on Saturday acknowledged the airstrikes had forced its troops to retreat and accused western forces of choosing sides.

"This is the objective of the coalition now, it is not to protect civilians because now they are directly fighting against the armed forces," Khaled Kaim, the deputy foreign minister, said in the capital, Tripoli. "They are trying to push the country to the brink of a civil war."

The rebel turnaround is a boost for US President Barack Obama, who has faced complaints from lawmakers from both parties that he has not sought their input about the US role in the conflict or explained with enough clarity about the American goals and exit strategy.

Pentagon officials are looking at plans to expand the firepower and airborne surveillance systems in the military campaign, including using the Air Force's AC-130 gunship armed with cannons that shoot from the side doors, as well as helicopters and drones.

US Defense Secretary Robert Gates said he could not offer a timetable for how long the Libya operation could last, as the Obama administration tried to bolster its case for bringing the United States into another war in the Muslim world.

Fox, the British foreign minister, ruled out supplying arms to the rebels. "We are not arming the rebels, we are not planning to arm the rebels," he said.