An official in Kyiv tells the BBC the “special operation” is an economic blow to Russia.
An explosion at a major gas export terminal near the city of St Petersburg in Russia was carried out by Ukrainian drones, BBC News has been told.
The blast caused a large fire at the Ust-Luga terminal, but no injuries, Russian officials said.
An official source in Kyiv said the “special operation” of the SBU security service masterminded the attack, with drones that worked “on target”.
Both Russia and Ukraine have used drones in the current conflict.
Russia launched its full-scale of invasion of Ukraine nearly two years ago, but has made little progress in recent months.
Regarding the explosion near St Petersburg, regional governor Alexander Drozdenko said a “high alert regime” was in place after the incident at the terminal of gas producer Novatek, in Ust-Luga on the Gulf of Finland. He shared a video of what appeared to be a large fire.
Novatek later announced that work at the terminal had been suspended, and said the fire was the result of “external influence” – without providing further details.
The Ukrainians say fuel processed at the plant was being used to supply Russian troops in their war against Ukraine and that this strike “significantly complicates” logistics for the military.
They also describe the attack as an economic blow to Russia, which exports fuel from the terminal.
Russia’s Fontanka.ru has published video showing tankers moored close to where the fire is raging. It reports two drones were spotted approaching the city of St Petersburg at about 01:00 local time (22:00 GMT) but swerved sharply at the outskirts before heading for the coast and the Ust-Luga port.
An eyewitness is heard saying the ground shook beneath his feet with the explosions.
The Russian Telegram channel Mash quotes a source saying they heard two explosions before the fire. The channel says around 150 staff were evacuated from the terminal.
Another video – posted on Russian social media – appears to show huge balls of orange fire, a man’s voice is heard referring to hearing the buzzing of a drone before the explosion.
Fontanka.ru, usually a reliable source, says flights in and out of St Petersburg had been grounded before the explosions, as a plan known as “Carpet” was put in place.
Russia’s defence ministry also said it shot down three Ukrainian drones in Smolensk Region, close to its border with Ukraine, on Saturday night.
It earlier said it had shot down drones over Tula and Oryol, both in western Russia. There were no reports of casualties.
Also on Sunday, at least 25 people were killed and 20 injured by shelling at a busy market in the Russian-controlled city of Donetsk in eastern Ukraine, Russian-installed officials said. Kyiv has not yet commented on that attack.
Russia and Ukraine have been targeting each other’s energy infrastructure, and on Friday a fire broke out at an oil depot in Bryansk, south-west Russia, which Moscow blamed on a Ukrainian drone strike.
That came a day after an attack targeted a major oil loading terminal in St Petersburg.
On Thursday, Russia claimed to have captured a village close to the devastated city of Bakhmut, in Ukraine’s eastern Donetsk region. Kyiv has not confirmed the claim.
Ukraine has warned repeatedly that its army is facing severe ammunition shortages, but has set a target of producing a million drones domestically this year.
Russia launched the invasion of its neighbour nearly two years ago.