Video footage showed a blaze at the Sudzha facility, which is located inside Russia several hundred metres from the Ukrainian border.
It is inside a pocket of Russian territory that had been captured by Ukrainian forces last year, but which Moscow has mostly recovered in heavy fighting in recent weeks. Russian troops pushed Ukrainian forces out of the nearby town of Sudzha last week.
Russia's defence ministry on Friday said Ukraine's troops had left the pumping station and blown it up in their retreat. Moscow described this as a violation of the moratorium on attacks on energy infrastructure, which it said it has abided by since a phone call between President Vladimir Putin and US President Donald Trump on Tuesday.
Kyiv said Russian forces had blown up the facility themselves as a provocation, describing Russia's accusations as fake.
Putin agreed to the pause in attacks on energy facilities during his phone call with Trump, when Putin rejected a proposal for a more comprehensive 30-day ceasefire. Kyiv says it is prepared to accept the proposal if hammered out formally in talks.
Russia's Investigative Committee, which probes serious crimes, said it had opened a criminal case over what it called "an act of terrorism" which had done "significant damage" to the gas transit facility, which once took Russian gas to Europe.
The Ukrainian military accused Russian forces of shelling it with artillery in a false flag "provocation".
"The Russians continue to produce numerous fakes and seek to mislead the international community," the Ukrainian army General Staff said in a statement.
Andriy Yermak, the Ukrainian president's chief-of-staff, said: "Russian attempts to deceive everyone and pretend that they are 'adhering to the ceasefire' will not work, as the fake (news) about the strikes on the gas station will not work."
Kremlin spokesman Dmitry Peskov said the idea that Russia would destroy its own energy infrastructure was "absurd."
Reuters could not independently verify the accounts of the situation at the plant or the cause of the blast.
Peskov said earlier on Friday that Putin's order for Russian forces to temporarily halt attacks on energy infrastructure in Ukraine remained in force, and the Sudzha explosion showed Ukraine could not be trusted to keep its word.
Separately, a new explosion rocked an oil depot in Russia's southern Krasnodar region on Friday where firefighters had been trying to extinguish a blaze that had broken out on Tuesday after a Ukrainian drone attack hours after Putin spoke to Trump.
"During the extinguishing process, due to depressurisation of the burning tank, there was an explosion of oil products and release of burning oil," Russian regional authorities said on the Telegram messaging app.
The fire spread to another tank, and the fire area increased to 10,000 sqm, they added - more than twice the original size of the blaze. More than 450 firefighters were trying to tackle it, and two had been injured.
Russia has pounded Ukraine's energy grid throughout the war, causing frequent blackouts affecting civilians and industry, arguing that civilian infrastructure is a legitimate target because it helps Ukraine's war effort.
More recently, Kyiv has also been launching attacks on Russian oil and gas targets, which it says provide fuel for Moscow's forces in Ukraine and funds Russia's military.
