Among those victims, at least 147 were killed by airstrikes against neighborhoods under the control of opposition factions such as al-Kalasa, al-Moghayer and al-Ansari in Aleppo.
Other 162 civilians, including 43 minors and 38 women, perished by rockets and gas cylinder missiles launched by Islamic State against government-held towns like al-Zahra, al-Midan and al-Sulaymaniya.
Additionally, 11 people were killed by Syrian regime artillery in several towns in Aleppo, and another was killed by a sniper in the al-Zabdie neighborhood.
The London-based NGO said four civilians were killed by armed Islamist organizations shelling against the Shiite-dominated Shaikh Maqsoud area.
Meanwhile, snipers of the Syrian Democratic Forces killed two people in Helik neighborhood in Aleppo.
Another six victims, including three children, died in the explosion of a mortar factory in al-Sukkari town.