A Ukrainian drone attack Tuesday killed three people in the Russian border region of Belgorod, local authorities said, while a Russian attack killed one in central Ukraine.
A major oil refinery in southern Russia was also set ablaze, triggering a local state of emergency as thick black smoke billowed over the coastal town of Tuapse.
"Three civilians were killed following drone attacks by the Ukrainian armed forces," Belgorod regional governor Vyacheslav Gladkov wrote on Telegram, adding that three others were wounded.
The drones targeted a car, killing a man and a vehicle in another area where a man and a woman died, he said.
Since the start of its offensive in Ukraine in February 2022, Russia has been regularly bombing Ukraine, especially key infrastructure sites.
Russian attacks killed a 40-year-old man and wounded five more in the central Ukrainian city of Kryvyi Rig, the head of the wider Dnipropetrovsk region wrote on social media.
Kyiv says its attacks are mainly targeting Russian energy infrastructure to reduce Moscow's ability to finance its military.
The Tuapse oil terminal on Russia's southern Black Sea coast has been hit multiple times in recent weeks.
A fire raged at the site for several days last week after a Ukrainian drone attack, causing what locals called "oil rain" to fall from the sky.
Authorities ordered people to limit outdoor activity and close their windows as thick black streaks were left across the street, on animals and vehicles after the rain.