BEIRUT — Fighting in Syria's largest city of Aleppo stretched into its 11th day on Tuesday amid growing international condemnation of the Syrian government's crackdown on a tenacious rebellion that has lasted 17 months.

Activists reported renewed bombardments of rebel-held neighborhoods and clashes in many parts of Aleppo as the army pushed on with its offensive to retake this key northern city. The battle for Aleppo, Syria's commercial hub with around 3 million inhabitants, has now lasted longer than the rebel assault on the capital Damascus that regime troops crushed earlier in July.

Despite regime claims of success and repeated forays by tanks and ground forces into rebel-controlled areas in the northeast and southwest of the city, the rebels appear to have held their ground, prompting government forces to resort to more shelling by artillery and mortars. Rebel positions are also being attacked with helicopter gunships.