Rebels begin fighting in Tripoli

>>> good evening. as we come on the air tonight, there are some fast-moving developments in libya where it appears rebel fighters have begun the battle for tripoli , what may be their final push to topple the government of moammar gadhafi . there had been reports of gunfire and explosions in the capital this evening. but there's also confusion over the whereabouts of gadhafi himself amid persistent rumors he may have fled the country. american officials say they are hearing the exact same rumors but cannot confirm them. let's get right to our chief foreign correspondent, richard engel is in thanh, libya.

>> reporter: good evening, lester. rebels started firing wildly in the air when they heard the reports that gadhafi had left the country. but even the rebels here do not know if those reports are true. we can confirm that fighting has begun inside tripoli itself in at least three neighborhoods after the rebels made major advances earlier today. after a week of some of the most intense battles of the six-month revolution against moammar gadhafi , today, a key victory. the u.s. and nato-backed rebels took control of all of the city of zawia. when we arrived there today, the scars of the fighting were still fresh, buildings popped by bullets and partially collapsed, spent ammunition everywhere. and by our account, the bodies of at least five of gadhafi 's sub-saharan mercenaries -- the most intense fighting appears to have been at the only hotel, the jewel. this hotel is one of the tallest buildings here. gadhafi was using it as a base. the rebels have a renewed optimism. as we surveyed the damage, we saw a group of rebels, the same unit we followed on friday as they fought for this city. today they came to celebrate, libyan rebel style. a chaotic and somewhat dangerous barrage of anti-aircraft and weapons fire. these fighters are convinced this war is nearing an end. the top rebel commander in this area has told us that the zero hour, the final battle for tripoli , has now begun. lester?