Pro-Ukrainian fighters said they captured at least two Russian soldiers during a cross-border raid on Russian soil.
Denis Kapustin, leader of the Russian Volunteer Corps which is allied with Kyiv, paraded the alleged prisoners in a video filmed in what appeared to be the operations room of a hospital.
The move is another major escalation for a group causing mayhem in southern Russia and embarrassing the Kremlin by launching attacks in the country with apparent ease.
In the video broadcast on Sunday one of the prisoners was standing but the other was lying under a foil sheet on the operations table.
“As a gesture of goodwill, we are ready to give you these prisoners, ordinary Russian soldiers, for the opportunity to communicate with you personally,” Mr Kapustin said in a message directed at Vyacheslav Gladkov, the governor of Russia’s southern Belgorod region.
The fighters, Russian nationals who attacked from Ukraine for the second time in a week on Thursday, destroyed several buildings and caused hundreds of residents to flee.
Russia’s ministry of defence said that it deployed fighter jets and artillery to repel the attack, killing 30 fighters.
Mr Kapustin’s taunt appeared to undermine those claims, as did videos posted by the Freedom Legion of Russia, a group allied with the Russian Volunteer Corps, showing what it said were its fighters moving into the Russian border town of Shebekino.
Russian officials have said that the shelling of Shebekino and its outlying villages had intensified over the past week. Mr Gladkov ordered people to leave the area and also rejected the offer of a meeting with Mr Kapustin.
“I saw the appeal of scoundrels, murderers and fascists who allegedly want to meet with me,” he said as he declined the meeting in the border Village.
“There is a battle going on now in Novaya Tavolzhanka.”
Yevgeny Prigozhin, the head of Kremlin’s Wagner mercenary unit, responded by offering to send one of his senior commanders to the rendezvous instead.
Thousands of people have fled Shebekino, a city of 40,000 people, since Thursday. Many are now living in sports halls in Belgorod city or have been sent to neighbouring cities and regions.
They blame regional officials for ignoring deteriorating security in favour of projecting a sense of normality by hosting flower and dumpling festivals.
The incursions by pro-Ukrainian Russians, some of whom are known neo-Nazis, since Thursday appear to be the most serious since the start of the full-scale war in Ukraine, 15 months ago. Photos from Shebekino show burnt-out buildings.
A little-known group called the Polish Volunteer Corps has also said that it was involved in the attacks. The group has previously claimed to have fought around Bakhmut, the town in Ukraine’s eastern Donbas region where fighting has been fiercest.
Poland’s government has denied any links to the Polish Volunteer Corps, reports said.
In Ukraine, officials said that Russian missiles had hit an airbase near the city of Kropyvnytskyi, 200 miles south of Kyiv.
“The cruise missiles did not destroy everything,” a spokesman for the Ukrainian air force said. “But, unfortunately, they hit the operational Airfield.”
Ukrainian officials have said that the Kremlin has changed its tactics, targeting military command and logistics centres instead of civilian infrastructure, in a bid to disrupt Ukraine’s counteroffensive.
On Sunday, local media reported several TV channels in Russian-occupied Crimea had been hacked to show a video of Ukraine’s defence ministry saying it would not announce the start of the counteroffensive.
Meanwhile, a two-year-old girl was also killed yesterday in Ukraine and 22 people were injured in a separate Russian missile attack near Dnipro.
And across Russia, police detained 45 people for protesting against the imprisonment of Alexander Navalny, perhaps Russia’s most high-profile opposition leader. His supporters had called for people to protest on his 47th birthday.