Having already reshaped the battlefield by doing work once reserved for long-range missiles, field artillery and human intelligence, drones are now fighting Russian drones - a boon for Ukraine's dwindling stock of air defence missile systems.

Ukraine’s Security Service said its drones destroyed one jet and damaged four at Saki military airfield overnight, aiming to weaken Russia’s war capability in the occupied Crimea and on the Black Sea.

Early on Sunday a massive oil depot fire was raging near Russia's Black Sea resort of Sochi - blamed by the Russian authorities on a Ukrainian drone attack. Sochi's airport in the same area - Adler district - suspended flights.