All non-critical infrastructure in Ukraine's southern port city of Odesa was without power after Russia used Iranian-made drones to hit two energy facilities, officials said on Saturday, with much of the surrounding region also affected.

"Due to the scale of the damage all users in Odesa except critical infrastructure have been disconnected from electricity," Odesa mayor Gennadiy Trukhanov wrote on Facebook.

Ukraine's Prosecutor General's office said two power facilities in Odesa region were hit by Iranian-made Shahed-136 drones.

Ukraine's armed forces said on Facebook that 15 of those drones, which carry an explosive payload and fly into their target, had been launched on targets in the southern regions of Odesa and Mykolaiv, and that 10 had been shot down.

Odesa, Ukraine's largest port city, had population of over 1 million before Russia's Feb. 24 invasion.

A statement posted by the city administration on the Telegram app said that Russian strikes hit key transmission lines and equipment in Odesa region in the early hours of Saturday.

Moscow says three killed in Ukrainian drone attacks on air bases deep inside Russia

Odesa region governor Maksym Marchenko said Russia used 'kamikaze' drones, which fly into their target rather than firing munitions, and that two had been shot down over the Black Sea.

"As a result of the strike there is no electricity in almost all the districts and communities of our region," Marchenko wrote on Telegram.

Since October, Moscow has been targeting Ukraine's energy infrastructure with large waves of missile and drone strikes, with Kyiv acknowledging on Friday that every single thermal and hydro-electric power plant in the country had been damaged.

Ukraine says the attacks are war crimes due to their devastating effect on civilian life, while Moscow claims they are militarily legitimate.

Kyiv says Russia has launched hundreds of Shahed-136 drones at targets in Ukraine, and has called for tougher international sanctions against Iran in response.

Tehran denies supplying the drones to Moscow. Kyiv and its Western allies say that is a lie.

Britain's defence ministry said on Saturday that it believed Iran's military support for Russia was likely to increase in the coming months, including possible deliveries of ballistic missiles.