Ukrainian and Russian forces are engaged in “bloody battles” at the Azovstal steel plant, the last pocket of resistance in the pulverised city of Mariupol.

       The claim was made by a commander in the Azov regiment, Denis Prokopenko, who posted a brief video message posted to Telegram stating: “I am proud of my soldiers who are making superhuman efforts to contain the pressure of the enemy... the situation is extremely difficult.”

       The Ukrainians said Russian forces have pushed into the plant’s perimeter and were also bombing it from above. The Kremlin has denied there is any ground assault.

       Meanwhile, an adviser to Ukraine’s defence ministry said Azovstal has become “priority number one” for the nation’s political and military leadership.

       Yuriy Sak told the BBC that efforts were focused on defending the vast industrial complex and managing further evacuations. Humanitarian corridors to allow trapped civilians were expected to be put in place on Thursday.

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       Azovstal is the last holdout of Ukrainian resistance in the strategically important port city of Mariupol – which Mr Sak noted had become the “heart” of the war.

       Mariupol’s seemingly inevitable fall would deprive Ukraine of a vital port, allow Russia to establish a land corridor to the Crimean Peninsula, which it seized from Ukraine in 2014, and free up troops to fight elsewhere in the Donbas.

       It would also allow Russia’s leadership a prize to commemorate “Victory Day” on May 9, the date the country celebrates its defeat of the Nazis in World War Two.

       Mariupol, and the plant in particular, have come to symbolise the misery inflicted by the Russian invasion. The city has been pummelled during a two-month siege that has trapped civilians with little food, water, medicine or heat. Civilians holed up inside the plant have perhaps suffered even more. About 100 of them were evacuated over the weekend — the first time some saw daylight in months.

       In an early morning address, Ukraine’s President Zelensky said a truce would be needed in Mariupol to lift remaining civilians out of underground shelters and basements.

       “It will take time simply to lift people out of those basements, out of those underground shelters. In the present conditions, we cannot use heavy equipment to clear the rubble away. It all has to be done by hand,” Mr Zelensky said.

       The Russian government said it would open another evacuation corridor from the plant during certain hours on Thursday through to Saturday.

       But there was no immediate confirmation of those arrangements from other parties, and many previous assurances from the Kremlin have fallen through, with the Ukrainians blaming continued fighting by the Russians.

       It is unclear how many Ukrainian fighters are still inside the plant, but the Russians put the number at about 2,000 in recent weeks, and 500 were reported to be wounded. A few hundred civilians also remain there, the Ukrainian side said this week.

       The United Nations announced that more than 300 civilians were evacuated Wednesday from Mariupol and other nearby communities.

       A satellite image shows damage at the Azovstal steelworks in Mariupol after Russian forces began storming the bombed-out steel mill

       (AP)

       The evacuees arrived in Zaporizhzhia, about 140 miles (230 kilometres) away, where they were receiving humanitarian assistance.

       “Many came with nothing but the clothes they were wearing, and we will now support them during this difficult time, including with much-needed psychological support,” said Osnat Lubrani, the UN humanitarian coordinator for Ukraine.

       An assessment by the Washington-based Institute for the Study of War said Russian forces were struggling to gain traction in the Donbas. “Ukrainian defences have largely stalled Russian advances in eastern Ukraine,” it said.

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       The Kremlin on Thursday accused the West of preventing a “quick end” to Russia’s military campaign, specifically pointing out weapons and intelligence provided by the US, UK and Nato.

       It claimed to have killed over 600 Ukrainian fighters overnight.