It appears that large scale fighting has broken in southern Aleppo on 1 April, though it is currently unclear exactly how it started. The hostilities are centered around the government-held town of al-Eis, to the south of Aleppo city. Al-Eis has changed hands multiple times throughout the war, most recently last month, when Jabhat al-Nusra and Jund al-Aqsa briefly captured it before being forced out.
al-Nusra is featured prominently in the latest round of fighting, officially declaring the attack and posting multiple videos around al-Eis through its media wing. Most importantly, however, many rebel factions appear to be coordinating in the area, including FSA groups that are supposed to be involved in the nationwide ceasefire. Groups that are reportedly involved, besides Jabhat al-Nusra, include Ahrar al-Sham, Ajnad al-Sham, Levant Front, Faylaq al-Sham, Jaysh al-Fatiheen, the FSA Central Division, Jaysh al-Tahrir, Liwa Suqour al-Jabal, Division 13, and Jaysh al-Nasr, several of whom are vetted TOW groups. While some rebels have claimed this to be a counter attack, it is also being reported that 4,000 fighters are taking part in fighting on the rebel side, making it appear to be an organized offensive.