President Volodymyr Zelenskiy said Ukraine had launched an incursion into Russian territory to "restore justice" and pressure Moscow's forces, in his first acknowledgement of Kyiv's surprise offensive into the western Kursk region.
Moscow's forces on Sunday were in their sixth day of intense battle against Kyiv's largest incursion into Russian territory since the start of the war, which left southwestern parts of Russia vulnerable before reinforcement started arriving.
Russian authorities rushed to evacuate residents and imposed a sweeping security regime in three border regions on Saturday, while Belarus, a staunch ally of Moscow, sent more troops to its border with Ukraine, accusing Kyiv of violating its air space.
In his nightly video address, Zelenskiy said he had discussed the operation with top Ukrainian commander Oleksandr Syrskyi, vowing to respond in kind after Russia launched its full-scale invasion of its neighbour in February 2022.
"Today, I received several reports from Commander-in-Chief Syrskyi regarding the front lines and our actions to push the war onto the aggressor's territory," he said late on Saturday.
"Ukraine is proving that it can indeed restore justice and is ensuring the exact kind of pressure that is needed - pressure on the aggressor."
Russia's defence ministry said on Sunday it had destroyed 14 Ukrainian drones and four Tochka-U tactical ballistic missiles overnight over the Kursk region, and 18 drones over other Russian regions that Ukraine frequently attacks.
In a statement, it called the ground incursion, which military analysts say caught the Kremlin off-guard, "barbaric" and said it made no military sense.
Ukraine has at most occupied several tens of square kilometres of Russian territory without laying claim to it, while Russia controls more than 100,000 sq km of Ukraine's internationally recognised territory.
Russia's top general, Valery Gerasimov, said on Wednesday the attacks had been halted, but Russia has not pushed the Ukrainian forces back over the border.
Russian military bloggers said the situation had stabilised after Russia's reinforcements, though they said Ukraine was swiftly building up forces.
INJURIES AND EVACUATIONS
Early on Sunday, Kursk officials said 13 people were injured in the city after debris from a destroyed Ukrainian missile fell onto a nine-storey residential building.
An image posted by Kursk's mayor showed flames rising through a shattered apartment block surrounded by charred debris.
It was not clear whether there was further damage. Moscow and Kyiv rarely disclose the full extent of damage inflicted by attacks on them unless there are injuries or damage to residential buildings.
Alexei Smirnov, Kursk's acting governor, ordered local authorities to speed up the evacuation of civilians in areas at risk. On Saturday, Russia's TASS state news agency reported that more than 76,000 people had been evacuated.
Kyiv and Moscow deny targeting civilians in their attacks in the war, which has killed thousands of people and displaced millions of Ukrainians, and has no end in sight.
Russian military bloggers say fighting is taking place as deep as 20 km inside the Kursk region, prompting some of them to question why Ukraine was able to pierce the Kursk region so easily.
After a father and his 4-year-old son were killed in a Russian air attack near Kyiv on Sunday, Zelenskiy asked Ukraine's Western partners for "strong decisions" allowing his troops to strike deep inside Russia with Western weapons.
"When Ukraine's long-range capabilities have no limits, this war will definitely have a limit," he wrote on X.
Russian Human Rights Commissioner Tatyana Moskalkova said she had sent an appeal to the United Nations demanding it condemn Ukraine's actions in Kursk.
In a Telegram post, Moskalkova said she was asking the U.N. Human Rights commissioner to "take measures to prevent gross mass violations of human rights".