Air strikes hit rebel-held parts of Aleppo just hours after a temporary truce announced by Russia came into effect in the northern Syrian city.
The British-based Syrian Observatory for Human Rights said the strikes on June 16 hit neighborhoods in opposition-held territory in Aleppo.
Rebels also fired rockets into the government-held sector, it added.
Russia, an ally of Syrian President Bashar al-Assad, announced late on June 15 that a regime of calm had been introduced in Aleppo "with the goal of lowering the level of armed violence and stabilizing the situation."
It did not say if any other parties to the conflict had been consulted.
Russia has provided air support to troops loyal to the Syrian regime as they battled the militant group and other Syrian rebels located in Aleppo.