France's President Emmanuel Macron has confirmed that two French aid workers died in a Russian strike in Ukraine, condemning the attack as "outrageous".
Ukrainian officials said the men were killed in a recent drone attack in the south of the country yesterday.
"Two French aid workers have been killed in Ukraine by a Russian strike. A cowardly and outrageous act," President Macron said on social media.
"My solidarity goes out to all the volunteers who are committed to helping people," he added.
Foreign Minister Stephane Sejourne said: "Russia will have to answer for its crimes."
"Russian barbarity has targeted civilians in Ukraine. Two French humanitarian workers paid for their commitment to the Ukrainians with their lives," he wrote on social media.
Deux humanitaires français ont été tués en Ukraine par une frappe russe. Acte lâche et indigne. Je pense à leurs proches et camarades blessés.
— Emmanuel Macron (@EmmanuelMacron) February 2, 2024
Ma solidarité va à tous les bénévoles qui s'engagent pour aider les populations.
Ukrainian officials had said that two French nationals were killed and three other foreigners wounded in Beryslav, near the southern Ukrainian city of Kherson.
Police in Ukraine said they had died as a result of a drone attack.
Beryslav, on the western bank of the Dnipro River in Kherson close to the front line, has regularly been targeted by Russian drones and artillery.
Kherson was abandoned by Russian forces in late 2022.
Ukrainian President Volodymyr Zelensky voiced gratitude for the Frenchmen's work in his war-torn country.
"Russian terror knows no boundaries or victims' nationalities.
"The brave French aid workers assisted people and we will always be grateful for their humanity.
"My condolences go out to their loved ones," President Zelensky wrote on social media.
In Paris, the prosecutors' anti-terrorist office announced that it had opened a war crimes investigation, specifically for an attack on an aid worker, non-combatants under international law.
La barbarie russe a visé des civils en Ukraine.
— Stéphane Séjourné (@steph_sejourne) February 2, 2024
Deux humanitaires français ont payé leur engagement auprès des Ukrainiens de leur vie. Trois sont blessés.
Mes pensées vont vers eux et leurs proches. La France se tient à leurs côtés. La Russie devra répondre de ses crimes.
Separately, tens of thousands of people were without power after a barrage of two dozen Russian drones damaged energy infrastructure in the centre of the country.
The overnight attack echoed the systematic bombardments by Russian forces last winter that left millions in Ukraine without power, heating or water for extended stretches.
The air force said Moscow had launched 24 Iranian-designed drones at Ukraine, where a national energy provider said its facilities in the Dnipropetrovsk region were damaged, adding that defence systems had downed 11.
"This led to a power outage for more than 40,000 subscribers," the head of the region, Sergiy Lysak, said on social media, adding that two mines were also without power.
The energy provider Ukrenergo said one of its substations in the city of Kryvyi Rig - President Volodymyr Zelensky's home town - was damaged during the attack.
Around 100 miners trapped underground had been brought out unharmed, regional officials said.
Mr Lysak also said a 37-year-old man was injured by Russian shelling on the village of Pokrovske.
In the northeastern Kharkiv region, authorities said around 64 towns and settlements had been left without electricity by Russian shelling.
Russia has also accused Ukraine of carrying out drone attacks on its territory.
Ukraine launched over a dozen drones at villages in Russia's border region of Belgorod over the past day, but no casualties have been reported, governor Vyacheslav Gladkov said.
