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.

In Sunday’s post on social media, President Zelensky described the latest Ukrainian strikes as “our long-range sanctions” against Russian facilities that he says finance Moscow’s war.

He said the Engels airfield and Saratov oil refinery were “strategic facilities”.

The Ukrainian military said in a separate statement that its attack triggered a blaze at the airfield – one of the main bases of Russia’s strategic aviation.

It said Tu-95MC and Tu-160 bombers were regularly using Engels to launch missile strikes against Ukraine.

Saratov regional Governor Roman Busargin admitted that “a drone attack caused damage to civilian infrastructure in Saratov and Engels”. He later said that two people were killed.

Separately, three people were reported killed in a Ukrainian drone attack on a civilian vehicle in Russia’s Udmurtia region, and another three in the Belgorod region bordering Ukraine.

In the Samara region, Governor Vyacheslav Fedorishchev described a strike on a Wildberries warehouse that caused a fire as “yet another terrorist act” by Ukraine.

The governor reported no casualties in the overnight attack.

In recent weeks, Ukraine has hit a number of Wildberries logistics hubs, describing them as legitimate targets providing the Russian military with drone components, navigation equipment and other gear.

Wildberries – often described as Russia’s Amazon – employs some 48,000 people.

Ukraine’s attacks are reported to have had a serious impact on the Russian economy, especially on hundreds of small and mid-sized businesses using the retailer.

Meanwhile, Russia has been recently targeting warehouses of Ukraine’s Nova Poshta postal company and major online retailers like Rozetka.

Rozetka said its largest warehouse was hit overnight by Russian drones, but reported no injuries.