Two Russian drones were suspected of flying over Nato country Romania to attack a port in Ukraine.
Two of the unmanned aircraft were also reported to have crossed into Moldova as part of the operation, and to have been blown up on its soil.
Kyiv said Moscow attacked Ukraine with 140 drones overnight, injuring one person in the Izmail district of Ukraine’s Odesa region that lies on the Danube River and borders Romania and Moldova.
Photos shared by the emergency services showed rescuers putting out a fire at the site of an attack, without specifying exactly where.
Ukrainian authorities often withhold precise information for what they say are wartime security reasons.
The southern region is a central hub for Ukraine’s Black Sea exports and its port facilities have been regularly attacked by long-range strikes throughout the war launched by Russia in February 2022.
Moldovan President Maia Sandu said two Russian drones had violated Moldova’s airspace and exploded in its territory, “putting Moldovan lives at risk”.
“Russia respects no borders, attacks civilians, spreads terror...Leave us, peaceful nations, alone,” she wrote on X.
Mihai Popșoi, Moldova’s foreign minister said the ministry would summon the Russian ambassador over the incidents.
Two drones were likely to have breached Romania’s airspace, the country’s defence ministry said.
It said a possible drone crash site had been detected and that it was conducting searches.
Out of 140 drones, the Ukrainian air force said it shot down 85 drones and 52 did not reach their targets likely due to electronic countermeasures.
The air strikes come after a major drone and missile attack on Kyiv.
Vladimir Putin does not appear to be easing back on military operations in Ukraine despite talks with Donald Trump on a peace deal to end the war.
The Russian president is also believed to be seeking to seize as much territory in Ukraine now even if it means his army suffering heavy losses.
Trump’s administration has signalled that it believes that annexed Crimea will remain in Russian control as part of a peace deal.
But this stance has sparked a backlash from some countries in Europe.
There has been an unprecedented use of drones in Putin’s war in Ukraine, launched nearly three years ago.
Some of the unmanned aircraft can fly more than 900 miles to hit targets.
Russian troops have taken control of the settlement of Vodiane Druhe in Ukraine's eastern Donetsk province, Russia's Defence Ministry said on Thursday.
