Russian forces mounted a furious assault on the Azovstal steel factory on Thursday after breaching Ukrainian perimeter defences, seeking to destroy the last pocket of resistance in the ruined city of Mariupol and allow Moscow to claim a victory ahead of a symbolically important Russian holiday.

“It has been two days since the enemy broke into the territory of the plant,” Lieutenant Colonel Denys Prokopenko, a Ukrainian commander, said in a video posted overnight. “Heavy, bloody battles are raging.”

A few hours later, Petro Andriushchenko, an adviser to the city government, said that there had been non-stop shelling overnight and into the morning. The last patch of Ukrainian resistance beneath the hulking remains of what had once been one of Europe’s largest steel plants has been “turned into hell”, he said.

Ukrainian fighters have successfully defended the plant from a direct assault for weeks. But Russian forces managed to find their way into the four-square-mile complex with the help of a former worker familiar with its layout, according to Anton Gerashchenko, an adviser to the ministry of internal affairs.

Gerashchenko, on social media and speaking to reporters, said that an electrician who worked at Azovstal showed the Russians the tunnels they could use to enter the complex. He tied the assault to a Russian desire to declare “victory” in Mariupol before the Monday holiday commemorating the Soviet Union’s triumph over Nazi Germany.

He said that is why the Kremlin recently dispatched Vladimir Solovyov, a national television host under sanctions by the West for his role in pushing Russian propaganda, to Mariupol.

In a sign of the city’s importance to Moscow, Russia is estimated by western military analysts to have committed 12 to 14 battalions of around 1,000 soldiers each to the fight for Mariupol, roughly 10 per cent of all its combat forces in Ukraine.

A senior Pentagon official said on Wednesday that only around two battalions remained, along with some units of Chechen fighters. The rest have been dispatched to the eastern front to be redeployed.

The decision to storm the factory could still prove costly — something President Vladimir V. Putin seemed to recognise when he ordered troops on April 21 to hold back from a full-on assault. Fighting inside tunnels creates challenges even for a technologically superior conventional force such as Russia’s, and could result in more casualties for Moscow’s troops, military experts say.

Ukrainian defenders in the city have exceeded the expectations of many outside observers — surviving despite being outnumbered, outgunned and cut off from resupply.

New York Times News Service