On Friday, Russia hosted ceasefire talks in a move to stop the escalation of violence in the separatist region of Nagorno-Karabakh.
After 10 hours of negotiations, both Armenia and Azerbaijan agreed to a truce starting on Saturday at noon.
But just moments after it came into effect, both sides accused each other of violating the terms.
On Sunday night, a residential building in Ganja, the second-largest city in Azerbaijan, was allegedly hit by an Armenian airstrike, killing nine and injuring at least 13, while Nagorno-Karabakh's military officials said that Azerbaijani forces shelled Stepanakert, the region's capital. Both sides denied the accusations.