The recent all-out rebel assault on regime-held west Aleppo was a huge shock, both to the regime fighters entrusted with holding the enclave as well as the hapless residents of that part of the city. The Islamist groups had been mustering their forces for quite some time. The coordinated offensive on several fronts was spearheaded by prominent jihadist groups, most notably the al-Qaeda affiliate Jabhat al-Nusra, and reportedly led by Chechens. It has featured a host of foreign fighters.
The Aleppo offensive began immediately after Islamist groups assaulted Kassab, in Latakia province, in late March, and it increased in ferocity in stages, culminating in a concerted effort by rebels to enter the Zahra suburb and lay siege to Air Force Intelligence headquarters in the northwest. The rebels also attacked the military academy on the Damascus highway to the northeast and attempted to sever the only road in and out of Aleppo via Khanaser in the Ramouseh area. In the past few days, rebels have also attempted to push through from the east of the city at Midan as well as in the old city. The assault would not have been possible without the withdrawal of the Islamic State of Iraq and al-Sham (ISIS) from most of Aleppo province. This resulted in the cessation of the interfactional war among Islamist rebels in the area, allowing them to concentrate instead on fighting the regime.