Monday’s incursion, apparently involving armoured vehicles, was the biggest raid into Russia since the war began 15 months ago, though details including the number of fighters involved, their affiliation and the extent of any clashes, could not be independently confirmed.
Russian authorities evacuated residents from the region’s Graivoron district after the raiding forces claimed to have captured the border town of Kozinka and several others.
“The cleansing of the territory by the Ministry of Defence together with law enforcement agencies continues,” Belgorod governor Vyacheslav Gladkov said on the Telegram messaging service.
“I now appeal to the residents of the Graivoron district, who … temporarily left their homes, it is not possible to return yet,” he said, adding that two buildings had been attacked by drones overnight.
Gladkov said one woman had died during the evacuation, and there were reports of two people wounded. The “number one” task on Tuesday was to reach them. On Monday, Gladkov had said at least eight people had been wounded, several buildings damaged and many residents had left.
One of the groups claiming responsibility for the incursion, the Freedom of Russia Legion, said on Telegram: “Good morning everybody, except Putin‘s henchmen. We have met the dawn on liberated territory, and are moving further on.”
It and a second group, the Russian Volunteer Corps (RVC), say they represent armed Russian fighters opposed to the Kremlin and operating from Ukraine.
Moscow blamed the attack on Ukrainian forces, saying saboteurs were seeking to deflect attention from Russia’s capture of the city of Bakhmut three days ago after the bloodiest land battle in Europe since World War Two.
Russian investigators said they were opening a terrorism case into the incursion.
Kyiv publicly denied blame for the raid, though some of its denials were pitched with apparent irony, to mimic past Russian denials of a role in separatist movements in Ukraine.
Kyiv “has nothing to do with it”, tweeted Ukrainian presidential adviser Mykhailo Podolyak. “As you know, tanks are sold at any Russian military store, and underground guerrilla groups are composed of Russian citizens.”
The RVC published video footage late on Monday showing what it said was a fighter inspecting a captured armoured vehicle, putting a sticker with the group’s logo over the “Z” symbol used to identify Russian forces. Another video showed what it said were fighters operating an armoured vehicle on a country road.
Other videos posted on Russian and Ukrainian social media channels showed pictures and video of what were described as captured Russian servicemen and their identity documents.
Mash, a Russian news channel on Telegram, said drones had struck the roof of the Russian FSB security service building in Belgorod city overnight, nearly 80 km (50 miles) from the district where the raid took place. It posted a picture of emergency vehicles outside the building.
Inside Ukraine, Russian forces are celebrating their first major victory in 10 months with the capture of Bakhmut. Kyiv says its forces have been making their own gains on the outskirts of the city to the north and south.
President Volodymyr Zelenskiy visited Ukrainian marines on Tuesday, positing pictures at an undisclosed location he said was on the front line.