Al-Jabha Al-Shamiya, or the Levant Front, - a recently-formed alliance of Syrian opposition groups - bombarded the camps of the regular troops and pro-regime militias, killing at least 15 soldiers and militiamen.
The bombardment with 106 m.m. guns targeted the command of Brigade 80 on the outskirts of Aleppo city, north Syria, the Shaam news network (SNN) reported on Sunday.
The regime's Air Force hit back by launching a barrel bomb attack on Kafr Naha town in Aleppo governorate.
The attack killed a civilian and wounded five others; all from one family, according to the SNN report.
In Al-Zabadani city, to the northwest of Damascus near the borders with Lebanon, the opposition groups engaged with the regular troops in fierce battles and killed 20 soldiers.
The regime's warplanes dropped at least 30 barrel bombs on the city, Khan Al-Sheikh camp and Arsal Al-Ward, SNN added.
In a related development, the Syrian Observatory for Human Rights (SOHR) said it documented 2,683 deaths in January, 2015, a record low in the monthly death toll of the armed conflict in 31 months.
The victims include 750 civilians - including women and children, 1,135 opposition fighters - including foreign fighters, 382 soldiers and 10 members of the Lebanese Hezbollah group and other pro-regime militias.