Ukraine has destroyed Russian strategic bombers in an unprecedented undercover drone operation while Russia launched its biggest-yet air raid on Ukraine’s cities and intensified attacks on its northern region of Sumy,

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.

President Volodymyr Zelenskyy said Defense Minister Rustem Umerov would sit down with Russian officials at the second round of peace talks on Monday.