A wave of almost 600 Ukrainian drones attacked Russia overnight killing four people, authorities said on Sunday, as Ukrainian President Volodymyr Zelensky called the barrage an "entirely justified" retribution for Moscow's own pummelling of Ukraine.

Air defences shot down 556 drones overnight across the country, Russia's defence ministry said, with another 30 drones intercepted after dawn in one of the largest Ukrainian barrages of the ongoing conflict so far.

These interceptions”? far above the few dozen more often reported”? took place across 14 Russian regions, as well as the Crimean peninsula annexed from Ukraine and the Black and Azov seas, the ministry added.

Ukrainian President Volodymyr Zelensky said Kyiv's attack on Russia”? days after a massive drone and missile bombardment of the Ukrainian capital killed at least 24 people”? was "entirely justified".

"Our responses to Russia's prolongation of the war and its attacks on our cities and communities are entirely justified. This time, Ukrainian long-range sanctions reached the Moscow region, and we are clearly telling the Russians: their state must end its war."

Ukraine's priority "remains the consistent build-up in the use of long-range strike capabilities to the fullest extent possible against a wide range of military targets," Commander of Ukraine's Unmanned Forces, Robert Brovdi, told AFP in a recent, exclusive interview before the strikes.