If successful, it would be the biggest blow to opposition fighters in Syria's largest city since they entered it two years ago. Aleppo, once Syria's commercial center, has been carved up into rebel- and government-controlled areas since an opposition offensive in mid-2012.
The push also comes a month after extremist fighters of the Islamic State group seized territories straddling Syria and neighbouring Iraq where they have declared a self-styled caliphate. Most of the land was seized in June during a push across Iraq.
Abdurrahman and an activist based near the city who goes by the name of Abu al-Hassan said Monday's fighting was concentrated near an army base known as the Infantry Academy that rebels captured two years ago.
"The latest attack does not mean that Aleppo will fall. It is going to be a very difficult battle," said Abdurrahman, whose group has a network of activists around the country. He said the aim of government forces currently is to try capture Aleppo's northern district of Handarat to be able to further close in on rebels.
Syrian government forces last week seized the Sheikh Najjar neighborhood and a key industrial area, allowing them to choke off rebel-held parts of Aleppo.
