Graves of Russian Wagner mercenary group fighters are seen in a cemetery near the village of Bakinskaya in Krasnodar region, Russia (Picture: Reuters)

Russia’s mercenary company Wagner Group has been taking ‘astonishing’ losses during the savage fight for control of the Ukrainian city of Bakhmut.

Defence and security analyst Professor Michael Clarke explained the firm’s ‘human wave’ attack tactics, with squadrons of mostly prison recruits sent in one after another under threat of execution.

Each group is tasked with trying to leapfrog the one deployed before, slowly dragging the front line closer to the enemy.

Despite suffering devastating losses of up to 80%, Prof Clarke described how the conscripts ‘keep coming forward’ like something out of a zombie film ‘because if they go back they get shot’.

The White House revealed last week that more than 30,000 Wagner Group fighters have been killed in Ukraine, with half of those occurring in Bakhmut in the past three months.

National Security Council spokesman John Kirby told reporters the US estimates that 90% of the paramilitary group’s casualties since December have been convicts.

He said Wagner had recently made incremental gains, but those had taken many months to achieve and came at a ‘devastating cost that is not sustainable’.

The ‘PMC Wagner Centre’ during the official opening of the office block on the National Unity Day, in Saint Petersburg (Picture: AFP via Getty)

Explaining the organisation’s tactics, Prof Clarke told Sky News: ‘What they do, is they send an eight-man squad into an area, say 100m that they’re trying to take, called the storm troopers.

‘And they’re job is to go in until they’re fired on. As soon as they come up against fire and make contact, they drop to the ground and start digging furiously.

‘Then artillery starts ahead of them to try and clear the ground ahead. And then the next eight men go in, and they’re called the musicians, for reasons I can’t fathom.

‘They drop into the trenches the first group has dug, and they start digging as well. Then a third group go in. And each group tries to leapfrog the other, digging trenches as they go forward.’

Prof Clarke rubbished Wagner’s claim of using four squads of eight to take a position, saying the real figure was more like ’10 or 12 or 15 squads’.

He went on: ‘What Ukrainians are telling journalists and the rest of us is that sometimes they are committing 80 or 100 troops and they’re losing, say, 60 or 70 of them and they still keep coming forward, because if they go back they get shot. They’re told that.

‘These are the convicts we’re talking about. Wagner’s recruited around 40,000 convicts. They’re told if you retreat, if you don’t keep going forward, you’ll get shot.

‘And anecdotally, the Ukrainians are telling us we see a group of six or seven, we drop a mortar shell amongst them and four of them go down, and the other three keep coming.

‘It’s astonishing, because they’re too frightened to go back anyway.

‘This is the “human wave” attack element. They’re taking up to 80% losses, and more than half of those losses have occurred in the past three months, most of it around Bakhmut. It’s ferocious.’

One Ukrainian solder, named as Andriy, told CNN earlier this month that fighting the Wagner Goup was like something out of a zombie film.

‘We were fighting for about 10 hours in a row. And it wasn’t like just waves, it was uninterrupted. So it was just like they didn’t stop coming,’ he said.

‘They’re climbing above the corpse of their friends, stepping on them.’

Wagner founder Yevgeny Prigozhin said on Friday the mercenaries have taken full control of Berkhivka, a village on the outskirts of Bakhmut.

It is roughly two miles northwest of the city’s suburbs.

Yevgeny Prigozhin, left, shows Russian President Vladimir Putin, around his factory (Picture: AP)

Prigozhin, a millionaire with close ties to Russian President Vladimir Putin, recently accused the military top brass of trying to ‘destroy’ the force by starving his fighters of ammunition.

He said this ‘can be likened to high treason in the very moment when Wagner is fighting for Bakhmut, losing hundreds of its fighters every day’.

Prigozhin has also repeatedly accused army chiefs of incompetence.

He has raised his public profile, issuing daily statements that boast about Wagner’s purported victories and mock his opponents.

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‘They’re told if you retreat, if you don’t keep going forward, you’ll get shot.’