Armed insurgents who crossed the border from Ukraine to launch attacks in Russia’s Belgorod region have been defeated, Moscow says.
Villages in the border region were evacuated after coming under sustained shellfire.
Russia says 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. The measures were lifted on Tuesday afternoon.
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 on 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.
But 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.