A major oil terminal in Russia's north-western city of St Petersburg was struck overnight by Ukraine, Volodymyr Zelensky has said.
The Ukrainian president described it as key "infrastructure that generates revenue for Russia's war". Ukraine also said a major Russian naval base in the region was hit.
St Petersburg Governor Aleksandr Beglov said the city had been under a "massive" drone attack, admitting the oil terminal was hit but saying there had been no casualties.
Ukraine has recently intensified its long-range drone attacks on Russia's critical energy infrastructure, causing widespread fuel shortages. Kyiv says nearly 43% of Russia's oil refining capacity has been "disabled" as a result.
The BBC has not independently verified this figure.
Ukraine says Russian oil and gas facilities are legitimate targets as Moscow relies heavily on fossil fuel exports to finance its full-scale invasion, which began in February 2022.
Russian President Vladimir Putin - who last week made a rare admission that fuel shortages had been caused by Ukrainian attacks - on Saturday signed into law a bill aimed at boosting supplies to the domestic fuel market.
Zelensky said on Saturday morning that the targets hit in St Petersburg and the surrounding region had been about 850km (528 miles) from Ukraine's border.
The extent of the damage was not immediately clear, but a video posted by the Ukrainian president showed a drone flying towards a target and a huge column of black smoke billowing from the area following the strike.
The BBC later verified that St Petersburg's oil terminal had been hit.
Ukraine's military described the terminal as "one of the largest" in Russia, capable of producing 12.5 million tonnes of petroleum products per year.
It also said it hit a key naval base of the Russian Baltic Fleet in Kronstadt.
Russia has not publicly commented on the claim.
Governor Beglov said that 72 Ukrainian drones had been shot down over St Petersburg and the wider Leningrad region.
He urged city residents to stay indoors until the drone threat was over and warned that mobile internet services may have also been disrupted.
More than five million people live in St Petersburg.
In a separate development on Saturday, Ukraine's military denied that the key eastern Ukrainian town of Kostyantynivka was now under full Russian control.
Military spokesman Maj Andriy Kovalyov told the BBC that "Kostyantynivka remains under the control of the Defence Forces of Ukraine".
He admitted that there had been "cases of infiltration by small infantry groups deep into the combat formations of our forces", but added that those groups were being identified and destroyed.
His comments came a day after Putin said that Russian control had been established over the town in June. The Kremlin leader provided no evidence to back up his claim.
Zelensky wrote on Telegram later on Saturday: "If Kostyantynivka is now under Russian control, then Putin will probably have no problem meeting me there and finding diplomatic solutions to finally end the war.
"But still, he will not cross the front line: the truth is very different from Putin's words."
Kostyantynivka is one of several heavily fortified towns that make up Ukraine's "fortress belt" in the eastern Donetsk region, most of which is occupied by Russia.
In its latest operational bulletin on Saturday afternoon, the Russian defence ministry said it had shot down more than 500 Ukrainian drones and missiles launched overnight and in the morning.
It described the Ukrainian attacks as an attempt by Zelensky to "distract the attention" of Ukrainians and "foreign sponsors" from the consequences of one of the biggest and deadliest Russian strikes on Ukraine's capital, Kyiv, on 2 July and also a "catastrophic failure" of Ukrainian forces in Kostyantynivka.
Ukrainian attacks on Russian civilian facilities "will not go unanswered", the ministry said.
Both sides - it would seem - want to gain the upper hand ahead of next week's Nato summit in Turkey.
On Saturday, Putin sent US President Donald Trump a congratulatory note to mark the 4 July celebrations in the US and calling for "constructive relations" between their countries.
The Russian leader had visited commanders wearing military fatigues the day prior, at which point he had made his claim about capturing Kostyantynivka.
Zelensky said Putin had chosen to lie to the world about the situation on the front.
Additional reporting by BBC diplomatic correspondent James Landale in Moscow
