STORY: Grainy aerial footage released on Sunday (June 4) by a militant group of Russians fighting on behalf of Ukraine purports to show its members storming into a suburb of the Russian city of Belgorod.
The Freedom of Russia Legion and another group, the Russian Volunteer Corps, have claimed they've conducted a number of cross-border raids into Russian territory from Ukraine.
Last week, Moscow said two civilians were killed during fighting.
In a video posted the Freedom of Russia's Telegram channel, a man identifying himself as the commander of the Russian Volunteer Corps said his fighters had captured two wounded Russian soldiers.
The man offered to exchange them in a meeting with Belgorod's regional governor.
The governor, Vyacheslav Gladkov, responded on his own Telegram channel. Gladkov said there was a battle going on with saboteurs and terrorists in a Russian border town.
He said he was willing to meet with the militants to ensure the return of captives, if they were alive. He gave the name of a border checkpoint and a time.
But later on Sunday the militant group said it would hand over the prisoners to Ukraine after the governor failed to turn up as promised.
Russia's invasion of Ukraine last year has in recent weeks and months come home to Russia.
Gladkov said Ukrainian forces shelled Belgorod over the weekend, adding that 4,000 residents were relocated for safety.
Ukraine has denied attacks inside Russia.
Meanwhile Russian bombardment of Ukrainian cities continues. Ukrainian officials said a Russian missile attack on the city of Dnipro killed a two-year-old girl and injured at least 22 people.
Reuters could not independently verify the report. There was no immediate reaction from Moscow.
The border skirmishes and airstrikes come as Ukraine readies an expected counter-attack against Russian forces occupying swaths of Ukrainian territory in the country's east.
Kyiv on Sunday made a plea for operational silence ahead of the assault, discouraging public speculation over when and where it might strike.