Russia has pledged to deliver a decisive response to border strikes by Ukrainian forces.
The Russian army will deal a "tough response" to Ukrainian attacks on its border regions, the foreign ministry in Moscow said on Sunday.
“A tough response from the Russian army will not be long in coming,” pointed out foreign ministry spokeswoman, Maria Zakharova.
Meanwhile, Ukraine's incursion continued for a sixth day on Sunday and is unprecedented for its use of Ukrainian military units on Russian soil.
The exact aims of the operation remain unclear and Ukrainian military officials have adopted a policy of secrecy, presumably to ensure its success.
Ukraine's President Volodymyr Zelensky has acknowledged that Ukrainian forces are fighting in Russia’s Kursk region, saying the ongoing incursion proves that Ukraine “can indeed restore justice and ensure the necessary pressure on the aggressor.”
In this regard, a senior Ukrainian official told AFP that “thousands” of its troops had been deployed to the operation.
Russia’s Defense Ministry said on Saturday that it had deployed troops to Belgorod, Kursk and Bryansk as a “counter-terror operation” in the region.
It said it had deployed the additional troops and equipment, including tanks, rocket launchers and aviation units to push back the Kiev forces invading the country.
Belarus, a staunch ally of Russia, has sent more troops to its border with Ukraine, accusing Kiev of violating its airspace.
Russia’s defense ministry published footage on Saturday of tank crews firing on Ukrainian positions in the Kursk region, as well as an overnight air strike, after it said Friday it had deployed yet more units to the border region.
Russia’s army appeared to acknowledge that Ukrainian units had driven deep into the country, saying it had hit enemy units near the villages of Tolpino and Obshchy Kolodez, which are around 25 km and 30 km from the Russia-Ukraine border.
It said on Sunday that its troops had “foiled attempts by enemy mobile groups with armored vehicles to break through deep into Russian territory.”
Russia’s defense ministry said it had downed 35 Ukrainian drones overnight over the Russian regions of Kursk, Voronezh, Belgorod, Bryansk and Oryol.
It said on Sunday that its air defense systems destroyed 35 UAVs flying over the Russian regions.
“During the past night, attempts by the Kiev regime to carry out terrorist attacks using fixed-wing type UAVs and Tochka-U tactical missiles against targets on the territory of the Russian Federation were thwarted,” the Defense Ministry said.
Russian “air defense systems destroyed 14 Ukrainian unmanned aerial vehicles ... over the territory of the Kursk region, 16 UAVs were shot down over the territory of the Voronezh region, 3 UAVs [were shot down] over the Belgorod region, and one UAV each was destroyed over the territories of the Bryansk and Oryol regions,” it added.
Russian President Vladimir Putin has downplayed the Ukrainian forces incursion, describing it as a “large-scale provocation.”
Since Russia launched its special military operation to liberate Donbas in February 2022, the US-led Western countries have flooded Kiev with huge supplies of Western weapons and ammunition.