MOSCOW, Russia -- Ukrainian helicopters have bombed a fuel storage depot in western Russia sparking a huge fire, the regional governor said Friday, in the first reported air strike by Kyiv on Russian soil.

The announcement came on the 37th day of Russia's military campaign in Ukraine, with thousands killed and more than 10 million displaced in the worst refugee crisis in Europe since World War II.

The strike in the Russian town of Belgorod marked the first time Russia has reported a Ukrainian airstrike on its territory since the conflict began.

"There was a fire at the petrol depot because of an air strike carried out by two Ukrainian army helicopters, which entered Russian territory at a low altitude," Belgorod region governor Vyacheslav Gladkov wrote on messaging app Telegram.

Two employees at the storage facility were injured in the fire, he said in another post.

Some 170 firefighters were battling to put out the enormous blaze, which started around 6 am (0300 GMT), the emergencies ministry said.

A massive fire was raging, with black and white smoke billowing overhead, a video released by the ministry showed.

Russian energy giant Rosneft, which owns the facility, said it had evacuated staff from the premises.

Long lines of cars waited at filling stations but the governor urged residents not to panic buy, saying there was enough petrol.

"There aren't any problems with fuel in the region and there won't be any," Gladkov said.

Earlier this week, explosions could be heard from an arms depot in Belgorod but the authorities did not provide any clear explanation for the blasts.

Belgorod lies around 40 kilometres (25 miles) from Russia's border with Ukraine and some 80 kilometres from the Ukrainian city of Kharkiv, which has been pummelled by Russian forces since Moscow sent troops to Ukraine on February 24.

Separately, the Russian defence ministry said that Moscow had destroyed six military facilities in Ukraine, including five depots containing ammunition, rockets and artillery weapons.