Ukraine said its drones hit a Russian research and production facility that supplies components for missiles, as Russia unleashed a fresh barrage of air attacks overnight.

Russia has bombarded Ukraine with the largest attack of the conflict, launching 479 drones overnight in a bold offensive, the Ukrainian air force said.

Across the country, swarms of small explosive drones descended onto military bases and destroyed a large part of Russia's nuclear bomber fleet. The flying bombs were smuggled into Russia by Ukrainian intelligence services in a plot known as Operation Spiderweb.