Ukraine has said it carried out overnight strikes deep inside Russia, hitting a major oil refinery and an airfield that houses Russian strategic aviation.

President Volodymyr Zelensky said the Engels airfield and the refinery, both in the Saratov region some 600km (373miles) from Ukraine’s border, were hit. An oil depot was also struck in Kaluga region and a drone launch site in Bryansk.

Russia said eight people were killed in the Ukrainian strikes, and 635 drones shot down or intercepted. It also reported yet another strike on a warehouse of Russia’s biggest online retailer Wildberries.

Meanwhile, Moscow said its forces attacked overnight two Ukrainian ports and two vessels in the Black Sea.

Later on Sunday, Ukraine said one person was killed in a Russian strike on a postal terminal near the north-eastern city of Kharkiv.

Both Russia and Ukraine have recently intensified attacks focusing on major cities, energy facilities and warehouses, as the vast front line remains virtually static and US-led mediation attempts to end the war have shown no breakthrough.

Russian President Vladimir Putin launched a full-scale invasion of Ukraine in February 2022.