Watch: pro-Russia region releases video of Azovstal steel plant bombing

The Interior Ministry of the separatist region Donetsk People's Republic has released video footage of Azovstal steel plant in Mariupol.

The video features military vehicles in the plant and a series of explosions hitting industrial buildings.

There was no information provided as to when the video was shot.

Heavy fighting raged Thursday at the shattered steel plant in Mariupol as Russian forces sought to finish off the city's last-ditch defenders and complete the capture of the strategically vital Ukrainian port.

The bloody battle came amid growing suspicions that President Vladimir Putin wants to present the Russian people with a major battlefield success - or announce an escalation of the war - in time for Victory Day on Monday. That is the biggest patriotic holiday on the Russian calendar, marking the Soviet Union's triumph over Nazi Germany.

Some 2,000 Ukrainian fighters, by Russia's most recent estimate, were holed up in the tunnels and bunkers under the sprawling Azovstal steelworks in Mariupol, the last pocket of resistance in a city largely reduced to rubble over the past two months. A few hundred civilians were also believed trapped there.

Capt. Sviatoslav Palamar, who as deputy commander of Ukraine's Azov Regiment led defenders inside the mill, told Ukrainian Channel 24 that Russian troops were inside the plant for a third day and meeting fierce resistance.

“Heavy fighting is underway," Palamar said.

The Russians managed to get inside with the help of an electrician who knew the layout, said Anton Gerashchenko, an adviser to Ukraine's Internal Affairs Ministry.

Also watch: Explained: Why is Russia continuously attacking Ukraine’s Mariupol

“He showed them the underground tunnels which are leading to the factory,” Gerashchenko said in a video posted late Wednesday. “Yesterday, the Russians started storming these tunnels, using the information they received from the betrayer.” The Kremlin denied its troops were storming the plant.

Mariupol's fall would be a major success for Moscow, depriving Ukraine of a vital port, allowing Russia to establish a land corridor to the Crimean Peninsula, which it seized from Ukraine in 2014, and freeing up troops to fight elsewhere in the Donbas, the eastern industrial region that the Kremlin says is now its chief objective.