Armed insurgents who crossed the border from Ukraine to launch attacks in Russia’s Belgorod region have been defeated, Moscow claimed.
Villages in the border region were evacuated after coming under sustained shellfire.
Russia said that 70 of the attackers have been killed and insists the fighters are Ukrainian.
But Kyiv has denied involvement and two Russian paramilitary groups have said they were behind the incursion.
Monday’s raid appears to have been the largest cross-border incursion since Russia’s full-scale invasion of Ukraine 15 months ago.
It led Moscow to declare a counter-terrorism operation in Belgorod, giving the authorities there special powers to clamp down on communications and people’s movements.
Russia’s defence Ministry said a “unit of the Ukrainian nationalist formation” invaded its territory and were responsible for heavy shelling on the Kozinka checkpoint and the Gravoronsky district in the Belgorod region on Monday.
In a statement published on Telegram Tuesday, the Ministry said 70 “Ukrainian terrorists” had been killed and the rest of the fighters had now been driven back to the Ukrainian border.
However, Ukrainian officials said those behind the incident were from groups called the Liberty of Russia Legion and the Russian Volunteer Corps (RVC).
“These are Russian patriots who want to change the political regime in the country,” Ukrainian Deputy Defence Minister Hanna Maliar told Ukrainian TV on Tuesday.
The Liberty of Russia Legion – a Ukraine-based Russian militia which says it is working inside Russia to overthrow President Vladimir Putin – said on Twitter on Monday it had “completely liberated” the border town of Kozinka.
It said forward units had reached the town of Grayvoron, further east.
The two paramilitary groups told Ukraine’s public broadcaster Suspilne Tuesday that they were creating “a demilitarised zone on the border with the Russian Federation from which they will not be able to shell Ukraine”.
Belgorod’s governor Vyacheslav Gladkov said several people had been injured in the fighting, including two civilians who were being evacuated from their homes.
Gladkov said that people in several villages had been evacuated and warned those who had fled their homes not to return yet, as Russian forces carried out what he described as a “mopping-up” operation.
He added that air defences had shot down drones overnight, damaging buildings.
It has been verified by BBC that a building used by Russia’s main security agency, the FSB, was among those hit. It is not clear what caused the damage.
BBC.