Russian drone strikes on Ukraine killed three people across the country, while Ukrainian attacks killed one near Moscow and targeted Russia's lucrative oil facilities, according to statements by the warring countries on Sunday.
The two neighbors have been firing hundreds of explosive-packed drones at each other on a daily basis throughout the four-year war, as talks to end the conflict have gone nowhere.
Russian attacks on Ukraine's southern Odesa region -- home to key export terminals -- killed two people, including a truck driver at a port, regional governor Oleg Kiper said on social media.
"Enemy drones hit three residential buildings, and two more were damaged.... Facilities and equipment for the port infrastructure were also damaged," AFP quoted him as saying.
The emergency services posted photos of firefighters tackling a blaze after the attacks.
Russian strikes on the frontline region of Kherson, in southern Ukraine, also killed one person, officials there said.
Russia fired 268 drones and one ballistic missile in the overnight attack, Kyiv's air force said.
Ukraine's army meanwhile launched at least 334 drones at Russia, Moscow's defense ministry said.
The northwestern Leningrad region was heavily targeted.
Oil export terminals there have been hit several times in recent weeks, knocking out billions of dollars worth of exports, according to Kyiv.
Oil and gas revenues -- boosted by the war in the Middle East -- are critical for Russia's economy and funding its army.
Ukrainian President Volodymyr Zelensky said two of Russia's so-called shadow tankers -- aging vessels that ferry its sanctioned oil around the world -- were struck off the southern Black Sea port of Novorossiysk.
He posted black-and-white night-vision footage of a naval drone approaching one tanker.
The damage done was unknown.
A Ukrainian drone attack also killed a 77-year-old man in the Moscow region, which surrounds the Russian capital, the regional governor said.
Kyiv calls its attacks on Russia fair retaliation for Russia's nightly barrages of its cities.
It says it only targets energy and military facilities.
Russia also denies targeting civilians.
Tens of thousands have been killed in the four-year war, unleashed by Russia's February 2022 invasion.
In April, Russia fired a record number of long-range attack drones at Ukraine -- an average of more than 200 a day -- according to AFP analysis of data from Kyiv's air force.
