Yevgeny Prigozhin, whose influence has risen hugely in Moscow's Ukraine offensive, has in recent days released a series of scathing videos attacking Russia's military leadership.

"Today one of the units of the defence ministry fled from one of our flanks... exposing the front," Prigozhin said in a video.

He has threatened to pull his fighters out of Bakhmut on May 10 if he did not receive badly needed ammunition.

The mercenary group has spearheaded Moscow's fight for the eastern Ukrainian city.

Prigozhin said soldiers were fleeing because of the "stupidity" of Russian army commanders, who he said were giving "criminal orders".

"Soldiers should not die because of the absolute stupidity of their leadership," Prigozhin said.

He released the video on Russia's Victory Day, when Moscow celebrates the Soviet victory over the Nazis in World War II.

Russia's defence ministry said in a statement later in the day that "assault troops" -- normally a reference to Wagner units -- were "continuing to fight in the western part" of Bakhmut.

The ministry said Russian paratroopers "provided assistance", without mentioning Prigozhin's accusation of soldiers abandoning their posts.

- 'Unable to defend Russia' -

In his unprecedented attack on the Russian army, Prigozhin said Tuesday that Moscow's top generals were trying to "deceive" President Vladimir Putin over the Kremlin's Ukraine campaign.

"If all the tasks are being carried out in such a way as to deceive the commander-in-chief (Putin), then either he will rip your arse or the Russian people will -- who will be angry that the war is lost," Prigozhin said.

As Ukraine prepares for a spring offensive, the outspoken 61-year-old questioned the Kremlin's ability to defend the country.

"Why is the state not able to defend its country?" Prigozhin said in the video, adding that Ukraine was hitting Russian border regions "successfully".

Prigozhin published the video as Moscow celebrated its Victory Day with a grand military parade on Red Square that was televised across the country.

He said Ukraine was preparing for an offensive "that will be on the ground, not on TV".

"So far, in our country everyone thinks that everything needs to be done on TV."

Russia has provided near round-the-clock coverage of its offensive, showing the army in an exclusively positive light.