Syrian government troops stepped up their campaign to drive rebels out of Aleppo Monday, but rebel fighters said they were holding firm and would turn the country's largest city into the "grave of the regime."

Opposition activists denied a government declaration that its forces had recaptured the Salaheddine district, in southwest Aleppo, which lies across the main route for Syrian troop reinforcements coming from the south, Reuters reported.

Hospitals and makeshift clinics in rebel-held eastern neighborhoods were filling up with casualties from a week of fighting in the city, a commercial hub drawn into the 16-month-long revolt against President Bashar al-Assad.

"Some days we get around 30, 40 people, not including the bodies," said a young medic in one clinic. "A few days ago we got 30 injured and maybe 20 corpses, but half of those bodies were ripped to pieces. We can't figure out who they are."

The opposition Syrian Observatory for Human Rights said 40 people, 30 of them civilians, were killed in Syria on Monday. Two rebel fighters died in Salaheddine.

Outgunned rebels, patrolling in flat-bed trucks flying green-white-and-black "independence" flags, said they were holding out in Salaheddine despite a battering by the army's heavy weapons and helicopter gunships.

"We always knew the regime's grave would be Aleppo," Mohammed, a young fighter, told Reuters, fingering the bullets in his tattered brown ammunition vest.

"Damascus is the capital, but here we have a fourth of the country's population and the entire force of its economy. Bashar's forces will be buried here."

So far, however, the government's superiority on the ground means rebels have had little success in holding on to urban territory. The rebels made a major push into Damascus two weeks ago, but were driven out.