KYIV >> President Volodymyr Zelenskiy acknowledged for the first time on Saturday that Ukrainian forces were fighting in the surprise offensive in Russia’s Kursk, as the border region’s authorities rushed to evacuate civilians from areas at risk.

Moscow’s forces are in their sixth day of intense battles 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.

In a sign of the gravity of the situation, Russia 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 restore justice after Russia launched a full-scale aggression on its smaller 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.

“Ukraine is proving that it can indeed restore justice and ensure the necessary pressure on the aggressor.”

Russian President Vladimir Putin cast the Ukrainian attack – which military analysts say caught the Kremlin off-guard – as a major provocation.

Russia’s top general, Valery Gerasimov, said on Wednesday the attacks had been halted, but Russia has thus far failed to push the Ukrainian forces back over the border.

Russian military bloggers say the situation had stabilised after Russia’s reinforcements, though they said Ukraine was swiftly building up forces.

Early on Sunday, Kursk officials said that 13 people were injured in the city after debris from a destroyed Ukraine-launched missile fell onto a nine-storey residential building.

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.

Both 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 that fighting is taking place as deep as 20 km (12 miles) inside the Kursk region, prompting some of them to question why Ukraine was able to pierce the Kursk region so easily.