One person died Saturday in the Russian border region of Belgorod adjoining Ukraine and a fire broke out at an oil refinery further east in Samara after drone attacks, officials said.

Belgorod governor Vyacheslav Gladkov wrote on Telegram that two districts in his region had been hit by drones.

"It's shaping up to be a difficult morning," Gladkov said. "One civilian was killed, two others were wounded."

The region of Samara, meanwhile, saw "several drone attacks" on local oil refineries, governor Dmitri Azarov said in a statement published on Telegram.

One of them caused a fire at the Kuibyshev refinery, he added, noting that there were no casualties.

The refinery, run by Russian oil giant Rosneft, is one of the largest in Samara, with a production capacity of seven million tonnes per year, according to its official website.

A drone attack on another refinery in the region, Novokuibyshevsk, "was repelled without damaging the technological equipment", according to Azarov.

"We see that the enemy, which is suffering defeats on the battlefield, is doing everything possible to undermine our endurance and unity," he said.

Separately, the Russian defence ministry said in a press release that it had destroyed "12 Ukrainian drones" overnight over the regions of Bryansk, Belgorod and Voronezh, all three of which border Ukraine, as well as over the region of Saratov.

Ukraine, which has been facing a Russian offensive for over two years, has stepped up its attacks inside Russia in recent weeks, targeting energy sites in particular.

Kyiv had promised to bring the fighting to Russian soil in retaliation for the numerous bombardments on its territory.