Fallujah, Iraq ? American forces have killed about 600 insurgents in their fight to retake Fallujah, the U.S. military said Thursday as troops pushed toward the city’s southern corridor, where the streets are lined with bombs and sniper hideouts.

The American military plans to have full control of Fallujah by Saturday, ending the bloody urban battle that’s killed 18 American troops and wounded 178 others, officials said. However, it appeared doubtful that the offensive’s goal — weakening the insurgency by wiping out its main refuge in time for January’s national elections — would be achieved, as violence spread unchecked to other key cities.

“If anybody thinks that Fallujah is going to be the end of the insurgency in Iraq, that was never the objective, never our intention and even never our hope,” Air Force Gen. Richard Myers, the chairman of the Joint Chiefs of Staff, said Thursday on NBC’s “Today” show.

Defense Secretary Donald Rumsfeld, on his way to El Salvador to kick off a Latin America visit, said the Fallujah operation would end successfully, but acknowledged that some insurgents might have fled the city before the invasion.

“I have no doubt that some people did leave before it started,” he said. “We also know that there are a number of hundreds that didn’t and have been killed. Others have been captured.”

In Baghdad, a powerful car bomb ripped through a traffic jam on a bustling commercial strip, killing at least 15 people and injuring dozens, according to police and medical workers. Many Iraqis burned to death in their cars or were crushed under rubble in the attack near major hotels housing foreign workers, witnesses said.

The blast punched a deep crater into the ground in front of Nasser Square, a busy intersection with a landmark statue of a former Iraqi prime minister. Rescue workers pulled blackened passengers from smoldering cars. Dazed, blood-spattered survivors said a gunfight had preceded the bombing.

“I saw a white, modern SUV passing very fast with a police car in front of it,” Jasim Adnan said. “I heard heavy shooting, and then the explosion happened. After that, I saw only a huge fireball and thick smoke.”

In other parts of the capital, gun battles between insurgents and American or Iraqi forces erupted for the third straight day. The clashes broke out in industrial areas, residential districts and the city’s sparsely populated outskirts. Often they took place in broad daylight, with bullets bouncing off the cars of Iraqis heading to work or running errands.

Violence aimed at Iraq’s new security forces continued, with masked gunmen storming several police stations and setting them ablaze in the restive northwest part of the country. The attacks were heaviest in Mosul, Iraq’s third-largest city, where insurgents roamed the streets with grenade launchers and U.S. warplanes streaked overhead.