The Russian military said on Tuesday it had routed militants who had attacked a Russian border region with armoured vehicles the previous day, killing more than 70 "Ukrainian nationalists" and pushing the remainder back into Ukraine.
Ukraine had attacked Belgorod. In Ukraine's biggest offensive in the war that began 15 months ago, two so-called anti-Kremlin armed groups employing Russians abroad said they were responsible for the attack.
Blaming Ukrainian authorities for the attack, Moscow's Defense Ministry said its forces had surrounded the enemy fighters and defeated them with "air strikes, artillery fire and active action by border units"
It said over 70 Ukrainian fighters had been killed, and four armored vehicles and five pick-up trucks destroyed, Reuters reported.
"The remnants of the nationalists were pushed back to Ukrainian territory, where they continued to be hit by gunfire until they were completely eliminated," it added.
One of the two groups - the Russian Volunteer Corps (RVC) - appeared to confirm on social media that its forces had withdrawn saying: "One day we'll come to stay."
Kyiv had said it was watching the situation but "has nothing to do with it", as it did in March when one of the groups - which Moscow said consisted of far-right Russian extremists managed by Ukrainian intelligence - mounted an incursion into another border region.
Former president Dmitry Medvedev, now deputy chairman of Russia's Security Council, was cited by Russia's RIA news agency as saying Kyiv's denial was "lies" and that the attackers deserved to be exterminated "like rats".