Watch: Russian mercenaries storm trenches and fight door-to-door in rare close combat footage

telegraph.co.uk: The Russian mercenaries advanced in single file, picking their way over rubble in the eastern town of Popasna as they approached their target: a cluster of houses containing Ukrainian defenders.

One fighter, purportedly from the mercenary Wagner Group, breaks away from the formation and approaches the house from the left. Then another, from the right.

A volley of grenades is thrown into a home with a green door and moments later around a dozen Ukrainian troops are seen lying on their bellies - prisoners of the Russian invaders.

The skirmish, which was filmed by a drone, purportedly shows the moment that Russia’s brutal Wagner Group captures a group of Ukrainian soldiers as Moscow seeks to encircle Kyiv’s forces in the east and north-east.

Wagner, which takes its name from the composer Richard Wagner, was founded in 2014 and has been accused of committing war crimes in Africa and Syria while on assignments for the Russian regime.

Posted online by a pro-Russian blogger, the footage from Popasna has not yet been verified, but it appears to confirm for the first time that Wagner has joined Russia’s eastern offensive.

Other extracts from the film, before the Ukrainian surrender, show one of their soldiers retreating from a trench as smoke billows around the ruined houses.

Popasna, the scene of the skirmish, along with the nearby city of Izium, is part of an intense battle for control of strategic areas of the Donbas region, where Russia is now concentrating its military efforts.

Russia has reportedly moved more than 20 battalion tactical groups [BTGs] close to Izium as it seeks to cut off Ukrainian forces in the Donbas region, in what could be a decisive moment for the war in Ukraine.

The British Ministry of Defence said on Wednesday that 22 BTGs had been deployed “near Izium” in a bid to capture two significant cities nearby, which would lay the groundwork for encircling Ukrainian forces.

Russian advances

However, the Russian advance on eastern Ukraine appears to have already stalled due to a combination of incompetence, poor morale, troop losses and the beginnings of a Ukrainian counter-attack.

“Despite struggling to break through Ukrainian defences and build momentum, Russia highly likely intends to proceed beyond Izium to capture the cities of Kramatorsk and Severodonetsk,” the Ministry of Defence said in its daily assessment of the war in Ukraine on Wednesday.

It added that “capturing these locations would consolidate Russian military control of the north-eastern Donbas and provide a staging point for their efforts to cut off Ukrainian forces in the region”.

Izium, which is occupied by Russian forces, lies around 70 kilometres south-east of Kharkiv, Ukraine’s second-largest city.

As the city sits on Russia’s northern axis of advance, it could be a staging area for an attempt to cut off and defeat the bulk of Ukraine’s soldiers in eastern Ukraine. This in turn would prevent reinforcements from being sent to other key Ukrainian cities such as Kyiv.

Decoy mannequins in uniforms

However, Western officials say Russia’s troop advances have already stalled in the Donbas region.

This is partly due to heavy losses in their failed attempt to capture Kyiv, as well as fierce resistance from Ukrainian troops armed with British and American weapons.

Russia’s army also appears to have been duped by the Ukrainian army’s diversionary tactics - recent video footage of a Russian artillery strike on a trench near Izium showed it was manned by decoy mannequins in uniforms.

Another video, posted online by Rob Lee, a military analyst at King’s College London, showed the moment a Russian artillery strike landed short of a Ukrainian trench in the same area.

“The position looks well-fortified and the soldiers are likely underground. Not clear whether these strikes are particularly effective without a ground assault,” the analyst observed on Twitter.

Separately, Ukrainian forces are said to have pushed the Russians around 25 miles east of Kharkiv in a counter-attack that could potentially unravel Moscow’s progress in the east.

New analysis by the Institute for the Study of War, a US think tank, says Russia could soon face a “dilemma” as to whether it should move back troops to reinforce Kharkiv or “risk losing most or all of their positions in artillery range of the city”.

“The Ukrainian counteroffensive may ... unhinge the Russian positions northeast of Kharkiv and could set conditions for a broader operation to drive the Russians from most of their positions around the city,” ISW researchers concluded.

Reports emerged on Wednesday that Russia’s morale and supply woes include soldiers from South Ossetia, the Russian-controlled breakaway state in Georgia.

According to MediaZona, an independent Russian news website that is currently blocked there due to its opposition to the war, some South Ossetian troops are refusing to fight in Ukraine and believe Russia will be defeated.

The soldiers reportedly complained of a lack of weapons and coherent orders, claiming that some artillery strikes missed by several kilometres and that they suffered frequent ambushes due to a lack of battlefield intelligence.

Meanwhile, the Ukrainian army released an intercepted recording of a Russian soldier boasting to his mother about the torture of Ukrainians. He discussed a method, which is too graphic to print, involving the mutilation of a prisoner's fingers and genitals.

Also on Wednesday, Russia claimed to have fired two Kalibr cruise missiles at Ukrainian targets from a submarine in the Black Sea and reiterated a warning that it would seek to hit shipments of Nato weapons to Ukraine.

The Russian defence ministry published video footage of the cruise missiles being launched from the Black Sea and said they had hit unspecified ground targets in Ukraine.

Russia previously said it had mounted similar strikes from a submarine on April 29.