BEIRUT, Lebanon — With tanks and artillery, the Syrian Army pounded opposition strongholds in Aleppo on Saturday, stepping up its barrage on a city that for days has been steeling for an assault, residents and activists said.

It was not clear whether the attack, which activists said was focused on the Salaheddiin neighborhood, was a limited foray by government troops or the beginning of a broader campaign.

Activists and residents said that the opposition had at least partly repelled the assault, killing soldiers and destroying several tanks, but those claims could not be immediately verified.

The clashes came after days of warnings from the international community about the human toll in Aleppo, Syria’s largest city and its commercial center, as President Bashar al-Assad’s forces massed on the outskirts of the city. For days, rebel fighters have been pouring into Salaheddiin and other neighborhoods in Aleppo, which had remained quiet for much of the uprising that started in March 2011.