BEIRUT – Syrian troops backed by warplanes battled rebels for control of a key highway in Damascus Saturday, a day after opposition forces cut the strategic artery as part of what they say are efforts to lay the groundwork for an eventual assault on the heavily defended capital.

Rebels have been on the offensive in Damascus since launching a series of attacks on government positions on Wednesday. They brought their fight to within a mile of the heart of the capital on Friday, seizing army checkpoints and cutting a key highway as they pressed their campaign for the city, the seat of President Bashar Assad's power.

The fighting is the heaviest to hit Damascus since July, when a first rebel assault managed to capture several neighborhoods before a punishing government counteroffensive. After that rebel foray, the regime quickly reasserted its control over the city, which has spared Damascus much of the violence and destruction that the civil war has wrought on other major urban centers.