Russia launched a "massive" missile attack on Ukraine overnight, damaging four power plants in its latest attack targeting the country's energy supply, officials in Kyiv said on Saturday.

Ukrainian President Volodymyr Zelensky called on Kyiv's Western partners to supply more air defense systems to protect his country's skies as the air force said it shot down 21 of 34 incoming missiles.

In recent months, Moscow has carried out some of the biggest attacks ever on Ukraine's energy facilities, knocking out much of its production and causing blackouts and energy rationing across the country.

Ukraine also said it struck two oil refineries and a military airbase in southern Russia in its own spate of overnight drone attacks.

“Thirty-four Russian missiles overnight. We managed to shoot down some of them. But the world has every opportunity to help (us) shoot down every missile and every drone,” Zelensky wrote in a message on Telegram.

Energy facilities were damaged in at least three regions, including Lviv and Ivano-Frankivsk in the west, hundreds of kilometers from the front line, Energy Minister German Galushchenko said in a Facebook post.

One of the missiles landed 15 kilometers (nine miles) from the Polish-Ukrainian border, Polish Prime Minister Donald Tusk said.

Kyiv says Moscow is stepping up air and land attacks ahead of nationwide celebrations on May 9, when Russia marks victory in World War II and Ukraine awaits the arrival of critical American weapons.

Energy operator DTEK said equipment at four of its thermal power plants was “severely damaged” as a result of the overnight strikes.

State electricity operator Ukrenergo said it had shut down a major overhead power line in the west of the country as a preventative measure.

Officials urged people and businesses to limit their electricity consumption.

“We ask all consumers to consume electricity sparingly. Industry is encouraged to maximize the import of electricity and use alternative energy sources,” Ukrenergo said in a statement.

The head of the western Lviv region called on residents not to use kettles, irons, washing machines and microwaves during evening rush hours.

At least two people were killed in separate attacks in the northeastern Kharkiv region and southern Kherson region, Ukrainian officials said.

More than a dozen were injured as a result of rocket and artillery attacks.

Russia's Defense Ministry said on Saturday that it had carried out 35 “group strikes” against Ukrainian energy facilities, military plants, railway facilities, air defense systems and other targets over the past week.

On Friday, the United States announced a $6 billion military supply package for Kyiv that will include key air defense ammunition and artillery shells.

At night, Ukraine launched a massive drone attack on the south of Russia, Krasnodar region.

A Ukrainian defense source told AFP that the strikes targeted two oil refineries and a military airfield in the region, east of the annexed Crimean peninsula.

“Ukrainian drones attacked the atmospheric distillation columns of the Ilsky and Slavyansky oil refineries. These are key technological facilities,” the source said.

Russian officials in the Krasnodar region reported a fire at an oil refinery in the city of Slavyansk-on-Kuban.

As a result, the plant partially suspended operations, Russian state media reported, citing a company representative.

Videos and photos on social media show a large fire raged at the site overnight following a series of explosions.

Moscow said Ukraine had launched one of the largest ever attempted drone attacks on the Krasnodar region.

“The air defense destroyed and intercepted 66 Ukrainian drones over the territory of the Krasnodar Territory and two over the Crimean Peninsula,” the Ministry of Defense reported.

The governor of Russia's Belgorod border region said later on Saturday that five people were injured when a Ukrainian drone fell on a road several kilometers from the border.

Kyiv has struck several oil refineries in western Russia in recent months, despite reports from Washington of concerns that the strikes could be seen as an escalation and could lead to a rise in global oil prices.

Ukraine says attacking Russia's vital energy sector is legal because it provides fuel and funds for the Russian military.