By Tom Balmforth and Olena Harmash

KYIV (Reuters) -Ukraine attacked eight Russian regions with dozens of long-range strike drones, setting ablaze a fuel depot and hitting three power substations in a major attack early on Saturday, an intelligence source in Kyiv told Reuters.

The overnight attack, which was confirmed by the defence ministry in Moscow, comes amid a Russian airstrike campaign that has battered Ukraine's energy system and pounded its cities in recent weeks.

Facing mounting pressure on the battlefield more than two years since Russia's full-scale invasion, Ukraine has tried to find a pressure point against the Kremlin by targeting oil refineries and energy facilities inside Russia using drones.

"At least three electrical substations and a fuel storage base were hit, where fires ignited," the Ukrainian source said, citing social media videos showing fires raging at different locations.

The source said the facilities were targeted for supporting Russian military industrial production.

Russia's defence ministry said it shot down 50 Ukrainian drones, including 26 in the Belgorod region, 10 in the Bryansk region, eight in Kursk region, two in Tula region as well as one in each of the regions of Smolensk, Ryazan, Kaluga and Moscow.

Vyacheslav Gladkov, the governor of Russia's Belgorod region which borders Ukraine, said two civilians were killed as a result of the attack.

The strike targeted a fuel energy facility in the western Smolensk region's Kardym region, hitting a reservoir with fuel and oil lubricants, the local governor confirmed.

"As a result of the work of air defence forces, the aircraft were shot down. However, as a result of falling debris, a tank with fuel and oil lubricants caught fire," he said, adding that firefighters were battling to put out the blaze.

It was not clear if anyone had been hurt, he said.

ALL EYES ON AID BILL

On Saturday, Ukrainians waited in anticipation for a vote in the U.S. House of Representatives later that could finally help unlock more than $60 billion in aid for Ukraine that has been held up for months.

Almost 26 months since the 2022 invasion, Russia is slowly advancing in eastern Ukraine and has ramped up its bombardments of cities and towns behind the front lines.

Just this year, Ukraine had been attacked by almost 1,200 missiles, more than 1,500 drones and 8,500 guided bombs amid a slowdown in Western military assistance, President Volodymyr Zelenskiy said on Friday.

Unable to rapidly produce long-range missiles and with limited access to those made by Western allies, Kyiv has focused on developing long-range strike drones to hit back. Russia has a sprawling arsenal of missiles and drones.

The overnight drone attack was a joint operation conducted by the Ukraine's SBU security service, the GUR military intelligence agency and the Special Operations Forces, the source said.