Russia's defence ministry said that 13 drones were destroyed overnight over annexed Crimea, six over the Belgorod region bordering Ukraine and an anti-ship missile was shot down over the region of Rostov, also bordering Ukraine.

In Rostov-on-Don city, dozens of emergency personnel rushed to put out the flames at the Novoshakhtinsk refinery, according to Governor Vasily Golubev.

"Following a drone strike, a fire broke out at the Novoshakhtinsk refinery," Golubev wrote on Telegram.

"Work was suspended due to a repeated attack, and personnel were withdrawn to a safe distance," he added.

He later clarified that the fire had been "localised" to an area of about 100 square metres (1,076 square feet), with no one immediately reported dead or injured.

The Novoshakhtinsk plant in the Rostov-on-Don region is considered one of the most important oil refineries in southern Russia. Located around 10 kilometres (six miles) east of the border, it is regularly targeted by Ukrainian attacks.

Representatives from the Russian Ministry of Emergency Situations and the regional emergency office headed to the scene of the blaze before dawn on Thursday, according to Golubev.

Another drone strike overnight destroyed an oil tank at a depot in Stary Oskol, north of the Ukrainian border, said Belgorod Region Governor Vyacheslav Gladkov.

That fire was "quickly extinguished" and there were no casualties, he added.

Ukraine, which has been facing a Russian offensive since February 2022, has upped its attacks on Russian territory in recent months.