A video shared on Twitter showed a blaze near apartment blocks in Belgorod, 40km (25 miles) from the border.

Some clips appeared to show rockets hitting the oil depot.

Ukraine's top security official, however, denied Ukrainian forces were behind the attack.

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"For some reason, they are saying we are behind it. This does not correspond to reality," security council secretary Oleksiy Danilov said.

Ukrainian aircraft have not struck targets in Russia previously.

Yet Belgorod governor Vyacheslav Gladkov accused Ukraine of launching the attack, and later Russian defence ministry spokesman Igor Konashenkov gave details.

He said that at around 05:00 Moscow time (02:00 GMT) two Ukrainian Mi-24 helicopters entered Russian airspace at extremely low altitude and "launched a missile attack on a civilian oil storage facility" on the outskirts of Belgorod. Some storage tanks were damaged and caught fire, he said.

"The oil storage facility has nothing to do with the Russian armed forces," he said.

President Vladimir Putin's spokesman said the incident "cannot be perceived as creating comfortable conditions for continuing the talks" with Kyiv. So far those peace talks have made little progress.

The spokesman, Dmitry Peskov, said Russia was now trying to reorganise the fuel supply chain to prevent disruption of Belgorod's energy supplies.

The city of 370,000 lies just north of Ukraine's second city Kharkiv, which has been heavily shelled by Russian artillery and remains surrounded by Russian forces.

Governor Gladkov said in a Telegram message that nobody was killed at the oil depot, which is run by Russian state oil firm Rosneft. He said emergency workers were trying to contain the fire and there was "no threat" to residents. The emergencies ministry posted video of the blaze on Telegram.

Russia's Interfax news agency reported that residents nearby were evacuated and two people were injured at the depot. It said eight fuel tanks were on fire and nearly 200 firefighters were on the scene.

Queues of cars later formed at local petrol stations, but Mr Gladkov said Belgorod's fuel supplies were still plentiful

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