Clashes broke out on Monday in Russian villages near the Ukrainian border, according to local officials and verified videos, after a group of anti-Kremlin Russian fighters allied with Ukraine appeared to have mounted a rare ground assault inside Russia.
Videos posted online and verified by The New York Times showed the aftermath of an attack on a border post near Grayvoron, a town in the Russian region of Belgorod, north of the eastern Ukrainian city of Kharkiv.
One video showed several soldiers and three armored vehicles, including one bearing an insignia previously seen on Ukrainian equipment, around a damaged building. Another showed a soldier and an armored vehicle bearing Ukrainian markings at an intersection about three miles into Russian territory. A third video appears to show the pro-Ukrainian fighters capturing a Russian armored vehicle.
A group called the Free Russia Legion, which says its ranks are made up of Russians, claimed to be behind the attacks. The group operates under the umbrella of Ukraine’s International Legion, a fighting force overseen by Ukrainian officers. Ukrainian officials sought to cast the unit’s action on Monday as proof of division among Russians, but it was not clear if the group acted on its own initiative or if Ukrainian officers had directed the attack.
The Ukrainian government, which typically follows a policy of deliberate ambiguity about strikes inside Russian territory, said it had not been behind the attack. An adviser to President Volodymyr Zelensky of Ukraine, Mykhailo Podolyak, said Kyiv was watching the events in Belgorod “with interest and studying the situation, but it has nothing to do with it.”
Ukraine’s military intelligence agency identified the attackers as “opposition-minded citizens of Russia.” Andrii Yusov, a spokesman for the agency, told Ukrainian media outlets that Russian partisans were working to create a security zone intended to protect Ukrainian civilians near the border.
The Russian regional governor, Vyacheslav Gladkov, said that a Ukrainian sabotage group had crossed the border near the city of Belgorod on Monday morning and that the Russian military, border service and intelligence agency were “taking the necessary measures to eliminate the enemy.” By Monday evening, he reported that eight residents had been injured.
The Free Russia Legion said it had “liberated” the border village of Kozinka — the location of the border crossing in the verified videos — along with another pro-Ukraine group known as the Russian Volunteer Corps. Those claims could not be independently confirmed, and it was unclear late Monday whether the groups’ fighters remained in Russian territory.
Reports of cross-border shelling from Ukraine on Monday morning gave way to fighting in the afternoon in several locations between the border and Grayvoron, a local administrative center about six miles from Kozinka, according to accounts published on Telegram.
Russia’s border in the area is well fortified with mines, trenches and barriers. Since the war began, Russian authorities have spent about 10 billion rubles — about $125 million — to strengthen the defenses of the Belgorod region, according to a statement by the regional construction minister to the Interfax news agency in February. The local government also established a Territorial Defense Unit to train citizens in military tactics.
Mr. Gladkov, the Russian governor, initially played down reports of violence, saying there was a “massive informational attack” underway, and sought to calm residents’ nerves in a video posted Monday morning. But by the evening, he said that he was putting the region on a counterterrorism footing, which gives the authorities wide power to establish temporary restrictions on movement, step up identity verifications and control telephone communications.
The Kremlin sought to downplay the incident, with its spokesman Dmitri S. Peskov telling the Tass news agency that it was a Ukrainian attempt to “divert attention from the situation” in Bakhmut, the eastern city that Russian forces claimed over the weekend to have captured after a nearly yearlong battle.
While there have been numerous reports of Ukrainians shelling targets across the border over the course of the 15-month conflict, ground assaults are rare. In early March, the Russian Volunteer Corps claimed it had staged a brief incursion into villages in Bryansk, another Russian region on Ukraine’s border.
The Russian Volunteer Corps is led by a Russian nationalist in exile, and is part of a motley collection of groups of Russian citizens who oppose President Vladimir V. Putin’s rule and have taken up arms for the Ukrainian cause.
Russia has suffered several significant psychological blows during the war, including the explosion that damaged the bridge linking the occupied Crimea peninsula to the Russian mainland and the sinking of the cruiser Moskva, the flagship of the Black Sea fleet. But Andriy Zagorodnyuk, a former Ukrainian defense minister who now advises his government, said this border incursion was a milestone because it involved armed troops, which could force Russia to deploy more of its forces along the border instead of the front lines.
It could also erode Russian unity, he said.
“Russians will see they have problems between their own citizens, so the idea of unified Russia is seriously damaged,” Mr. Zagorodnyuk said.
Oleksandr Chubko, Oleg Matsnev Milana Mazaeva and Riley Mellen contributed reporting.
