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.

Primary oil processing at Russia's Novokuibyshevsk refinery, which is operated by the Rosneft oil company, has been halted since August 2 following a Ukrainian drone attack last week, two industry sources said.

An overnight Ukrainian drone attack on an oil depot near Russia's Black Sea resort of Sochi sparked a major fire, Russian officials said Sunday, as the two countries traded strikes and the Ukrainian president announced a prisoner exchange.