Russia said Tuesday it had deployed jets and artillery to destroy an armed group that penetrated the border from Ukraine, while the Kremlin demanded the military prevent any repeat attack.
The incursion was the most serious since Moscow launched its large-scale offensive in Ukraine last year, prompting the Kremlin to express "deep concern" and the evacuation of nine villages in the southern region of Belgorod.
The Defense Ministry's announcement that it resorted to the air force and artillery on Russian territory confirmed an unprecedented use of force domestically since the offensive began.
"In the course of the counter-terrorist operation, the nationalist formations were blocked and destroyed by air strikes and artillery fire," the Russian ministry said.
"The remaining (fighters) were driven back to the territory of Ukraine, where they continued to be hit by fire until they were completely eliminated," it said.
Authorities said 12 people had been injured with the Belgorod region coming under sustained artillery and mortar fire during the fighting.
Moscow reported Russian forces killed more than 70 Ukrainian fighters and destroyed four armored vehicles, but AFP was unable to independently verify the claims.
Kremlin spokesman Dmitry Peskov said Moscow needed to avoid further Ukrainian incursions into Russia and voiced "deep concern," calling for "more effort from us... so that this does not happen again."
'Deep concern'
Belgorod's Governor Vyacheslav Gladkov said civilians were evacuated from nine border villages in the region, which has previously faced shelling attacks that have killed dozens of people since Moscow launched its offensive last year.
In Moscow, 70-year-old engineer Sergei Rusakov said the border incursion should act as a wake-up call for Russians in the south of the country.
"I think Belgorod residents need to think — not to lie on the couch but scratch their heads and ask themselves, is everything normal in the Russian state?" he told AFP.
In Kyiv, 46-year-old advertising agent Sergiy said the incursion was evidence that both Russian and Ukrainian forces could launch offensive operations and that the outcome of the conflict could still be unpredictable.
"I really hope that what is happening is in favor of our victory — whoever did it," he said.
Members of two anti-Kremlin groups, the Freedom of Russia Legion and the Russian Volunteer Corps, have claimed responsibility while Kyiv denied involvement.
"We are not waging war on foreign territories," Ukrainian Deputy Defense Minister Hanna Malyar said.
In a video purportedly released by the Freedom of Russia Legion on Monday, a camouflaged spokesman, surrounded by armed men in fatigues, said: "Russia will be free!" — a slogan frequently used by Russian opposition activists.
Several drones struck houses and a government building overnight but no one was killed, said the governor.
Gladkov added Tuesday that it was too soon for residents who fled to return and said authorities would give the all-clear when it was safe.
'Guerrilla movement'
Russia said Monday its troops were battling a "sabotage" group that entered from Ukraine and introduced an "anti-terror regime" in the region of Belgorod, a first since the start of Moscow's campaign in Ukraine in February 2022.
However regional Governor Gladkov announced Tuesday the lifting of the regime.
Britain's Defense Ministry noted "Russia is facing an increasingly serious multi-domain security threat in its border regions, with losses of combat aircraft, improvised explosive device attacks on rail lines and now direct partisan action."
Ukrainian presidential adviser Mikhaylo Podolyak suggested that Russian "guerrilla groups" could be responsible.
The anti-terror regime gives special powers to security services with beefed-up security and communications surveillance.
A similar regime was in place in Chechnya between 1999 and 2009, when authorities battled insurgents during Moscow's second military campaign in the mountainous region.
The attack on Russia's region was reported ahead of a widely expected Ukrainian offensive, though President Volodymyr Zelensky has said his country is not yet ready.
Zelensky visits front
Russia has been reinforcing hundreds of kilometers of front line with tank barriers, trenches and troops.
Zelensky on Tuesday visited Ukrainian troops on the frontline in the eastern region of Donetsk, where Russian forces have concentrated their efforts to capture territory.
"Every day on the battlefield, Ukrainian marines prove that they are a powerful force that destroys the enemy, liberates Ukrainian land and performs the most difficult tasks in the most difficult conditions," Zelensky said.
"And we need more of this force. So, from today, we are significantly increasing the potential of the marines and creating a marine corps," Zelensky said.
