Ukraine launched a wave of drones at Russia in the early hours of Saturday, setting a fuel depot ablaze, officials said, as both sides accused each other of deadly attacks on civilians.
The governor of Russia's Belgorod region said cross-border Ukrainian attacks left at least three people dead, while a Russian strike killed two in Ukraine's northeast.
A source in Ukraine's defence sector told AFP Kyiv targeted eight Russian regions in the "large-scale" drone attack, which was aimed at "energy infrastructure that feeds Russia's military-industrial complex".
"At least three electrical substations and a fuel storage base were hit and caught fire," the source said, calling it a "joint operation" of Ukraine's SBU security service, army, and military intelligence.
Russia's defence ministry said it had intercepted 50 Ukrainian drones overnight, some of them hundreds of kilometres from the border, including near the capital Moscow.
Video on social media purportedly showed a large blaze burning at a fuel depot in Russia's western Smolensk region, an attack that the governor confirmed was caused by drones.
"Air defence forces shot the aerial vehicles down. However, as a result of falling debris, a tank with fuel and lubricants caught fire," governor Vasily Anokhin said.
Kyiv has ramped up strikes on Russian oil and gas facilities in recent months, part of what it calls "fair" retaliation on infrastructure used to fuel Russia's war.
Ukrainian drones left two people in Russia's Belgorod border region dead, its governor said early Saturday, while shelling later in the day killed a pregnant woman.
A residential building and a barn in the village of Poroz, less than two kilometres (one mile) from the frontier, were "completely burned down", governor Vyacheslav Gladkov said. Another building was severely damaged.
"As a result of the release of two explosive devices, a private residential building caught fire. Tragically, two civilians died -- a woman who was recovering from a fractured femur, and a man who was caring for her," Gladkov wrote on Telegram.
He later said Ukraine shelled the village of Novaya Tavolzhanka, killing a pregnant woman and her unborn child.
"Doctors did everything possible to save both mother and child. But to the great grief, the woman and the unborn baby died from their wounds," he said.
Ukraine meanwhile said Russia launched strikes at residential buildings in the northeastern city of Vovchansk, killing two people and injuring two others.
"A direct hit was recorded on a nine-storey residential building. A woman and a man were injured. Both victims are 61 years old. At other addresses, two men aged 50 and 84 died as a result of shelling in the city," regional prosecutors said.
The region's governor, Oleg Sinegubov, shared a photo showing a pile of rubble next to the collapsed section of a multi-storey residential block.
Russia fired at least seven missiles at Ukraine overnight, two of which were shot down by air defences, Ukraine's air force said.
Ukraine has in recent months pleaded for more air defences from its Western allies as it struggles to fend off a surge in deadly attacks on civilian infrastructure.
The strike on its northeast comes a day after President Volodymyr Zelensky urged NATO to quickly deliver more aid to help his struggling forces, which have ceded ground to Russia in recent months.
"This year, we can't wait for decisions to be made," he told NATO defence ministers.
"We need seven more Patriots or similar air defence systems -- and it's a minimum number. They can save many lives and really change the situation," Zelensky said.
