Ukraine’s security service released footage Wednesday of its attack on Russian war planes at multiple airbases across the country. In the span of a few hours on Sunday, nearly a third of Moscow’s strategic bomber fleet was destroyed or damaged with cheaply made drones sneaked into Russian territory, according to Ukrainian officials.

The second recent round of direct discussions, in Istanbul, resulted in an agreement to trade more prisoners, but produced few steps toward ending the fighting.

Ukrainian and Russian delegations are set to meet again in Istanbul, Turkey, on Monday to take part in the next round of U.S.-brokered peace talks.